Gari.pk
Spark Plugs: All The Details You Need To Know
Spark Plugs: All The Details You Need To Know
divtext-align: center""Spark Plugs
Spark plugs have been around almost as long as the internal combustion engine. In 1902, spark plugs were first used with a high voltage magneto to provide reliable ignition. For the next 70 years, spark plugs were a high maintenance item thanks to tetraethyl lead, which was used as an octane-boosting additive in gasoline. Unfortunately, lead tended to foul spark plugs after 12,000 to 15,000 miles of driving. Consequently, tune-ups and spark plug changes were an annual ritual for most motorists.
Then came the Clean Air Act of 1970, followed by new emissions regulations and the introduction of catalytic converters in 1975. Leaded gasoline was gradually phased out because of its damaging effects on converters as well as the environment. As a result, spark plug life more than doubled.
In the mid-1980s, spark plug manufacturers started making plugs with copper core center electrodes. Copper is an excellent conductor of heat and allows plugs to run hotter without causing preignition. This improves fouling resistance, ignition reliability and plug life. It also reduces the number of plugs needed to cover a range of engine applications because each plug has a broader "heat range."
The biggest improvement in spark plug technology, though, came in 1985 when the first generation "long life" plugs with platinum or gold-palladium electrodes hit the market. Up to this point, electrode wear usually dictated when a set of plugs had to be replaced. With standard nickel alloy electrodes, the spark gap between the center and ground electrodes grows about .0002" to .0006" for every 1,000 miles of driving. After 35,000 miles of driving, the gap can grow as much as 0.015" or more.
Every time a spark plug fires, the hot spark blasts a few molecules of metal off the electrodes. As the miles add up, the electrode gap widens and the center electrode becomes rounded and dull. This increases the firing voltage needed to jump the gap. Eventually the point is reached where the ignition system can't generate enough juice to jump the gap, causing the plug to misfire.
With platinum, gold-palladium and other exotic metals (more on this in a minute), electrode wear is greatly reduced. Most platinum plugs can go up to 100,000 miles before they have to be replaced. The same is true for plugs that use other exotic metals such as iridium for their center electrode. Plugs with platinum on both electrodes ("double" platinum plugs) experience even less wear than plugs with only a single platinum or platinum-tipped electrode.
Long-life spark plugs drastically reduce the need for maintenance while helping the engine maintain like-new performance and emissions. Not having to change the plugs so often is a real savings for the vehicle owner, but it's no guarantee the plugs will go the distance.
Platinum & Iridium Spark Plugs
Long-life spark plugs by ACDelco, Autolite, Bosch, Champion, NGK and Split-Fire all have platinum or platinum-tipped electrodes. With a couple of exceptions, most of these plugs use a conventional electrode configuration with a small platinum plug welded to the tip of one or both electrodes. ACDelco also offers a platinum version of its "Rapidfire" plug that features a fluted center electrode for improved ignition reliability. Likewise, Split-Fire offers a platinum version of its split electrode plugs for motorists who want extended life as well as reduced misfiring.
Bosch, who introduced the first platinum plug back in 1985, offers several different electrode configurations in their product line. Their standard platinum plug has a thin pure platinum center electrode with a single yttrium-alloy end electrode. Their Platinum+2 and Platinum+4 plugs, on the other hand, have a unique "surface gap" side electrode design with two side electrodes on the Platinum+2 plug and four on the Platinum+4 - a sort of good, better, best approach to platinum plug technology. Increasing the number of side electrodes gives the spark more paths to ground and reduces the risk of misfire, while extending plug life by spreading wear over more electrode surfaces.
One important point to keep in mind with respect to Bosch Platinum+4 and Platinum+2 plugs is that these plugs are pre-gapped at the factory to a uniform 1.6 mm setting and should not be re-gapped to the specifications for a standard spark plug. It's very difficult to get even spacing with multiple electrodes so install them as is.
NGK "Iridium IX" and Denso brand "Iridium Power" plugs use a different exotic metal for their center electrode: you guessed it, iridium. Alloyed with rhodium, the iridium electrode is six times harder and eight times stronger than platinum. Pure iridium also has a melting temperature that is almost 1,200� F higher than platinum, making it a very tough metal indeed. On late-model Toyota and Lexus applications, the OEM-recommended replacement interval for Denso iridium plugs is 120,000 miles.
The iridium plugs also have a very thin (0.6 mm to 0.7 mm depending on the plug) center electrode. The end electrode has a "U-Groove" that improves ignition reliability and wear resistance. Denso says their design reduces the required firing voltage up to 5,000 volts compared to a standard spark plug.
For performance applications, Denso has also developed Iridium Power plugs with a super narrow 0.4 mm center electrode. These plugs are engineered to improve ignition reliability under extreme driving conditions rather than longevity, so the recommended replacement interval for the iridium plugs with the super narrow 0.4 mm center electrodes is 30,000 miles.
Here's another bit of trivia for the gray matter: Iridium is literally an out-of-this-world metal. Approximately 50 million years ago, according to the Denso website, a giant asteroid from outer space smashed into our planet near the Mexican town of Chicxulub in Yucatan. The impact created a firestorm and dust cloud that darkened the Earth for years, wiped out the dinosaurs and left us with a layer of iridium-rich deposits that is evenly spread across every continent (the "K/T boundary" layer).
Spark Plug Electrode Magic
Spark plug manufacturers tout the advantages of their unique electrode designs, but regardless of the design, the purpose is to make it as easy as possible for the plug to fire reliably. A spark jumps more easily from a sharp edge than a rounded blunt edge. So the more sharp edges it has to jump to, the better the odds of the plug firing under all types of driving conditions. The electrodes on some spark plugs are also designed to "unshroud" the spark so more of the spark will be exposed to the air/fuel mixture. This improves the propagation of the flame kernel once the fire is lit.
One thing to keep in mind with respect to performance claims is that no spark plug creates horsepower out of thin air. A special electrode configuration can reduce misfiring and the voltage needed to fire the plugs. But the spark only ignites what is already in the combustion chamber. If there are any power gains to be had, they will be the result of reduced misfires and nothing else.
New Spark Plugs Getting Smaller
Another trend in the ongoing evolution of spark plugs is that plugs are shrinking. The new Ford Triton engines use long-reach 10 mm plugs from Autolite, which are 4 mm skinnier than the 14 mm plugs you're used to seeing in most late-model engines. The threads on these plugs are also 1-3/8" above the end of the plug, so heat has a long ways to travel before it can be dissipated through the threads into the cylinder head. This requires a couple of tricks to manage heat. One is an unusual "U" shaped end electrode that wraps all the way over the end of the plug. Connecting both ends of the electrode to the plug shell creates two paths for heat to flow away from the tip. The end electrode is made of a special high temperature Inconel alloy. In the center of the "U" is a small platinum pad to reduce electrode wear when the plug fires. The center electrode is also platinum tipped and has a copper core to help pull heat away from the tip.
Autolite is also marketing a new "Titanium" spark plug. It's actually a standard spark plug with platinum tipped electrodes, but with a special titanium coating on the shell that resists seizing to reduce the risk of thread damage when changing plugs in aluminum cylinder heads.
Spark Plug Fouling Resistance
One thing all types of spark plugs must do is resist fouling. The trick here is to keep the electrodes hot enough to burn off fouling deposits but not so hot that they cause preignition. To burn off carbon deposits, the center electrode needs to reach about 700� F quickly. But if it gets too hot (above -1,500� F), it may ignite the fuel before the spark occurs, causing preignition and detonation. For most plugs, the ideal operating temperature is around 1,200� F.
The temperature of the electrodes is controlled by the length of the ceramic insulator that surrounds the center electrode and the design of the electrode itself. Ceramics do not conduct heat very well, so an insulator with a relatively long nose will conduct heat away from the electrode more slowly than one with a relatively short nose. The longer the path between the electrode and the surrounding plug shell, the slower the rate of cooling and the hotter the plug.
A spark plug's "heat range" (heat rating), depends on the length of the ceramic insulator and the design of the center electrode. The heat range must be carefully matched to the engine application otherwise the plugs may experience fouling problems at idle or run too hot under load causing preignition and detonation. Most plugs today have a relatively broad heat range thanks to the copper core center electrode described earlier. This allows the plugs to reach a self-cleaning temperature quickly and also prevents them from overheating.
Spark Plug Misfires
The voltage required to produce a spark can range from as little as 5,000 volts to as much as 30,000 volts or higher. The actual firing voltage will vary depending on operating conditions such as engine load, rpm, temperature, compression and the richness or leanness of the air/fuel mixture. The wider the electrode gap and the greater the load on the engine, the more voltage it takes to fire the spark plugs. Likewise, the higher the resistance in the spark plugs and plug wires, the higher the required firing voltage.
A cylinder may misfire if the spark never reaches the plug due to excessive resistance or breaks in the insulation in the plug wires, or a buildup of oxide, cracks or an excessively wide air gap inside a distributor cap. A weak coil or a faulty ignition module that doesn't give the coil enough time to fully charge between firings also can reduce the available firing voltage to the point where the spark may be too weak to jump the electrode gap. Of course, worn or dirty spark plugs also can make an engine hard to start, idle roughly, lack smoothness, waste fuel and pollute, too.
The most common cause of ignition misfire at the spark plug is fouling. A buildup of fuel and oil residue or other contaminants on or around the plug's electrodes can short out the spark before it reaches the gap. Contaminants also can form a barrier that blocks the gap or requires more voltage to punch through than the ignition system can deliver. The contaminants come from fuel additives as well as oil that gets past the rings and valve guide seals. A high-mileage engine with worn rings, cylinders and/or valve guides will often have a plug fouling problem.
On 1995 and newer vehicles with OBD II, ignition misfire will usually set a fault code and turn on the Check Engine light. Fuel that isn't burned causes a huge increase in hydrocarbon emissions and will usually cause a vehicle to fail an emissions test. Unburned fuel also can damage the catalytic converter by causing it to overheat. So if you find a cylinder-specific misfire code such as P0302 (indicating cylinder #2), check the spark plug, plug wire, coil (if it's a DIS or coil-on-plug system), fuel injector and compression to isolate the cause. On the other hand, if you find a random misfire code (P0300), the problem probably is not the ignition system. It's likely a lean fuel mixture caused by a vacuum leak or dirty injectors.
Spark Plug Service
As a rule, replacement spark plugs should have the same or better service interval as the original plugs. Long-life platinum and iridium spark plugs cost a little more than standard spark plugs and are an excellent upgrade for engines that were not originally equipped with these types of plugs. So replace same with same or better - unless an engine that was originally equipped with long-life spark plugs has a plug fouling problem due to high oil consumption. In this case, it doesn't matter what type of spark plugs you install because they won't last as long as normal. If the oil burning problem cannot be fixed, switching to a slightly hotter plug may help reduce fouling.
For performance applications, switching to a slightly cooler spark plug can reduce the risk of pre-ignition and detonation at high rpm and loads.
_____________________________________________
Choosing Racing Spark Plugs
Selecting the proper spark plugs for a performanc engine can mean the difference between front of the pack and a DNF. When using this guide, understand that race plugs are usually of a much colder heat range rating than standard automotive spark plugs. Colder spark plugs must be used in engines with increased cylinder pressures, higher temperatures and greater BHP. Other factors such as fuel delivery (turbo, supercharged), fuel types and piston-to-head clearance will also affect proper plug selection.
Step 1: Shell Design - The first step in choosing the proper race plug is determining the plug type that your cylinder head/piston will accept. Thread diameter and pitch, thread length and shell seat, as well as hex size are all factors that will define what shell type works best for your engine.
Step 2: Electrode Design - The second decision is electrode design and configuration. Is it a fine wire center or standard electrode? Projected or non-projected? Full coverage 'J-Gap' or perhaps a cut-back or angled ground wire? A good rule of thumb is to attain as much projection into the cylinder as possible. But be aware of piston clearance that could prohibit projected spark plugs from being used.
Step 3: Heat Range - The third factor in choosing a race plug is heat range. Correct heat range is critical in maintaining peak performance throughout the duration of your race or event. Switching to a colder or hotter plug will not increase horsepower, but could affect engine performance. Choosing a plug that is too hot can result in preignition or detonation. A plug that is too cold could cause an engine to stumble, misfire or foul.
The main factors to consider in selecting the proper heat range are: type of race, methanol, specific output, nitro-meth, compression ratio, nitrous oxide, horsepower, super or turbo charging and racing fuel.
Courtesy: Champion Spark Plugs
_____________________________________________
Spark Plug Replacement Tips
--Before you install any spark plug, compare the old and new plugs to make sure the replacement spark plugs have the same thread diameter, pitch (SAE or metric), thread length and seat configuration as the original plugs.
--On engines with aluminum heads, let the engine cool before you attempt to loosen and remove the plugs. This will reduce the risk of damaging the threads in the cylinder head.
--Always inspect the old spark plugs after they have been removed and note any conditions that would indicate a cylinder is running rich, lean or is burning oil.
--Spark plug wires should also be inspected - and replaced if the insulation is damaged, if resistance exceeds factory specifications or the boots are loose.
Courtesy NGK Spark Plugs, Inc.
_____________________________________________
Spark Plug Torque and Gap
How much the spark plugs should be tightened depends on the size of the plugs and the type of plug seat. Spark plugs with gasket-style seats require more torque than those with taper seats. Always follow vehicle manufacturer torque recommendations, but as a general rule:
14-mm plugs with a gasket-style seat should be tightened to 26 to 30 ft.-lbs. in cast iron heads, but only 18 to 22 ft.-lbs. in aluminum heads.
18-mm plugs with gasket-style seats should be tightened to 32 to 38 ft.-lbs. in cast iron heads, but only 28 to 34 ft.-lbs. in aluminum heads.
14-mm taper seat spark plugs should be tightened to 7 to 15 ft.-lbs. in both cast iron and aluminum.
18-mm taper seat spark plugs should be tightened to 15 to 20 ft.-lbs. in both types of heads.
As for setting the plug gap, always follow the vehicle manufacturer's recommendations - unless you are installing a set of Bosch's Platinum+4 spark plugs. These plugs are pre-gapped at the factory to a standard 1.6-mm gap. This is necessary to achieve maximum plug performance and longevity, so don't change the gap.
The reason is that the multiple ground electrodes in the Bosch Platinum+4 and Platinum+2 series are made from a special, wear-resistant nickel alloy, enhanced by the addition of yttrium-alloy. Not only do these plugs utilize factory set "surface air gap" technology that doesn't need gapping prior to installation, the manufacturer also said that the special alloys resist erosion so the gap maintains its correct setting for the life of the plug.
"Every time a spark plug fires, a tiny bit of metal is lost in the electrical discharge. Over time, this can degrade a plug's performance," said Otto Stefaner, general product manager, consumer products, for Bosch. "Multiple electrodes and precious metals minimize this degradation from metal transfer."
Stefaner also explained other benefits to their pre-gapped design. "Surface air gap technology also increases the electrode gap for better ignition, without increasing the voltage requirement, enabling the production of a larger flame core in the combustion chamber. Tests show that the four-electrode, platinum-core plugs transfer more energy efficiently to the air/fuel mixture. And plugs with four ground electrodes have up to 33% better cold restart reliability than conventional plugs," he said.
Courtesy Robert Bosch Corp.
3 Answers
399 views |
Spark plugs have been around almost as long as the internal combustion engine. In 1902, spark plugs were first used with a high voltage magneto to provide reliable ignition. For the next 70 years, spark plugs were a high maintenance item thanks to tetraethyl lead, which was used as an octane-boosting additive in gasoline. Unfortunately, lead tended to foul spark plugs after 12,000 to 15,000 miles of driving. Consequently, tune-ups and spark plug changes were an annual ritual for most motorists.
Then came the Clean Air Act of 1970, followed by new emissions regulations and the introduction of catalytic converters in 1975. Leaded gasoline was gradually phased out because of its damaging effects on converters as well as the environment. As a result, spark plug life more than doubled.
In the mid-1980s, spark plug manufacturers started making plugs with copper core center electrodes. Copper is an excellent conductor of heat and allows plugs to run hotter without causing preignition. This improves fouling resistance, ignition reliability and plug life. It also reduces the number of plugs needed to cover a range of engine applications because each plug has a broader "heat range."
The biggest improvement in spark plug technology, though, came in 1985 when the first generation "long life" plugs with platinum or gold-palladium electrodes hit the market. Up to this point, electrode wear usually dictated when a set of plugs had to be replaced. With standard nickel alloy electrodes, the spark gap between the center and ground electrodes grows about .0002" to .0006" for every 1,000 miles of driving. After 35,000 miles of driving, the gap can grow as much as 0.015" or more.
Every time a spark plug fires, the hot spark blasts a few molecules of metal off the electrodes. As the miles add up, the electrode gap widens and the center electrode becomes rounded and dull. This increases the firing voltage needed to jump the gap. Eventually the point is reached where the ignition system can't generate enough juice to jump the gap, causing the plug to misfire.
With platinum, gold-palladium and other exotic metals (more on this in a minute), electrode wear is greatly reduced. Most platinum plugs can go up to 100,000 miles before they have to be replaced. The same is true for plugs that use other exotic metals such as iridium for their center electrode. Plugs with platinum on both electrodes ("double" platinum plugs) experience even less wear than plugs with only a single platinum or platinum-tipped electrode.
Long-life spark plugs drastically reduce the need for maintenance while helping the engine maintain like-new performance and emissions. Not having to change the plugs so often is a real savings for the vehicle owner, but it's no guarantee the plugs will go the distance.
Platinum & Iridium Spark Plugs
Long-life spark plugs by ACDelco, Autolite, Bosch, Champion, NGK and Split-Fire all have platinum or platinum-tipped electrodes. With a couple of exceptions, most of these plugs use a conventional electrode configuration with a small platinum plug welded to the tip of one or both electrodes. ACDelco also offers a platinum version of its "Rapidfire" plug that features a fluted center electrode for improved ignition reliability. Likewise, Split-Fire offers a platinum version of its split electrode plugs for motorists who want extended life as well as reduced misfiring.
Bosch, who introduced the first platinum plug back in 1985, offers several different electrode configurations in their product line. Their standard platinum plug has a thin pure platinum center electrode with a single yttrium-alloy end electrode. Their Platinum+2 and Platinum+4 plugs, on the other hand, have a unique "surface gap" side electrode design with two side electrodes on the Platinum+2 plug and four on the Platinum+4 - a sort of good, better, best approach to platinum plug technology. Increasing the number of side electrodes gives the spark more paths to ground and reduces the risk of misfire, while extending plug life by spreading wear over more electrode surfaces.
One important point to keep in mind with respect to Bosch Platinum+4 and Platinum+2 plugs is that these plugs are pre-gapped at the factory to a uniform 1.6 mm setting and should not be re-gapped to the specifications for a standard spark plug. It's very difficult to get even spacing with multiple electrodes so install them as is.
NGK "Iridium IX" and Denso brand "Iridium Power" plugs use a different exotic metal for their center electrode: you guessed it, iridium. Alloyed with rhodium, the iridium electrode is six times harder and eight times stronger than platinum. Pure iridium also has a melting temperature that is almost 1,200� F higher than platinum, making it a very tough metal indeed. On late-model Toyota and Lexus applications, the OEM-recommended replacement interval for Denso iridium plugs is 120,000 miles.
The iridium plugs also have a very thin (0.6 mm to 0.7 mm depending on the plug) center electrode. The end electrode has a "U-Groove" that improves ignition reliability and wear resistance. Denso says their design reduces the required firing voltage up to 5,000 volts compared to a standard spark plug.
For performance applications, Denso has also developed Iridium Power plugs with a super narrow 0.4 mm center electrode. These plugs are engineered to improve ignition reliability under extreme driving conditions rather than longevity, so the recommended replacement interval for the iridium plugs with the super narrow 0.4 mm center electrodes is 30,000 miles.
Here's another bit of trivia for the gray matter: Iridium is literally an out-of-this-world metal. Approximately 50 million years ago, according to the Denso website, a giant asteroid from outer space smashed into our planet near the Mexican town of Chicxulub in Yucatan. The impact created a firestorm and dust cloud that darkened the Earth for years, wiped out the dinosaurs and left us with a layer of iridium-rich deposits that is evenly spread across every continent (the "K/T boundary" layer).
Spark Plug Electrode Magic
Spark plug manufacturers tout the advantages of their unique electrode designs, but regardless of the design, the purpose is to make it as easy as possible for the plug to fire reliably. A spark jumps more easily from a sharp edge than a rounded blunt edge. So the more sharp edges it has to jump to, the better the odds of the plug firing under all types of driving conditions. The electrodes on some spark plugs are also designed to "unshroud" the spark so more of the spark will be exposed to the air/fuel mixture. This improves the propagation of the flame kernel once the fire is lit.
One thing to keep in mind with respect to performance claims is that no spark plug creates horsepower out of thin air. A special electrode configuration can reduce misfiring and the voltage needed to fire the plugs. But the spark only ignites what is already in the combustion chamber. If there are any power gains to be had, they will be the result of reduced misfires and nothing else.
New Spark Plugs Getting Smaller
Another trend in the ongoing evolution of spark plugs is that plugs are shrinking. The new Ford Triton engines use long-reach 10 mm plugs from Autolite, which are 4 mm skinnier than the 14 mm plugs you're used to seeing in most late-model engines. The threads on these plugs are also 1-3/8" above the end of the plug, so heat has a long ways to travel before it can be dissipated through the threads into the cylinder head. This requires a couple of tricks to manage heat. One is an unusual "U" shaped end electrode that wraps all the way over the end of the plug. Connecting both ends of the electrode to the plug shell creates two paths for heat to flow away from the tip. The end electrode is made of a special high temperature Inconel alloy. In the center of the "U" is a small platinum pad to reduce electrode wear when the plug fires. The center electrode is also platinum tipped and has a copper core to help pull heat away from the tip.
Autolite is also marketing a new "Titanium" spark plug. It's actually a standard spark plug with platinum tipped electrodes, but with a special titanium coating on the shell that resists seizing to reduce the risk of thread damage when changing plugs in aluminum cylinder heads.
Spark Plug Fouling Resistance
One thing all types of spark plugs must do is resist fouling. The trick here is to keep the electrodes hot enough to burn off fouling deposits but not so hot that they cause preignition. To burn off carbon deposits, the center electrode needs to reach about 700� F quickly. But if it gets too hot (above -1,500� F), it may ignite the fuel before the spark occurs, causing preignition and detonation. For most plugs, the ideal operating temperature is around 1,200� F.
The temperature of the electrodes is controlled by the length of the ceramic insulator that surrounds the center electrode and the design of the electrode itself. Ceramics do not conduct heat very well, so an insulator with a relatively long nose will conduct heat away from the electrode more slowly than one with a relatively short nose. The longer the path between the electrode and the surrounding plug shell, the slower the rate of cooling and the hotter the plug.
A spark plug's "heat range" (heat rating), depends on the length of the ceramic insulator and the design of the center electrode. The heat range must be carefully matched to the engine application otherwise the plugs may experience fouling problems at idle or run too hot under load causing preignition and detonation. Most plugs today have a relatively broad heat range thanks to the copper core center electrode described earlier. This allows the plugs to reach a self-cleaning temperature quickly and also prevents them from overheating.
Spark Plug Misfires
The voltage required to produce a spark can range from as little as 5,000 volts to as much as 30,000 volts or higher. The actual firing voltage will vary depending on operating conditions such as engine load, rpm, temperature, compression and the richness or leanness of the air/fuel mixture. The wider the electrode gap and the greater the load on the engine, the more voltage it takes to fire the spark plugs. Likewise, the higher the resistance in the spark plugs and plug wires, the higher the required firing voltage.
A cylinder may misfire if the spark never reaches the plug due to excessive resistance or breaks in the insulation in the plug wires, or a buildup of oxide, cracks or an excessively wide air gap inside a distributor cap. A weak coil or a faulty ignition module that doesn't give the coil enough time to fully charge between firings also can reduce the available firing voltage to the point where the spark may be too weak to jump the electrode gap. Of course, worn or dirty spark plugs also can make an engine hard to start, idle roughly, lack smoothness, waste fuel and pollute, too.
The most common cause of ignition misfire at the spark plug is fouling. A buildup of fuel and oil residue or other contaminants on or around the plug's electrodes can short out the spark before it reaches the gap. Contaminants also can form a barrier that blocks the gap or requires more voltage to punch through than the ignition system can deliver. The contaminants come from fuel additives as well as oil that gets past the rings and valve guide seals. A high-mileage engine with worn rings, cylinders and/or valve guides will often have a plug fouling problem.
On 1995 and newer vehicles with OBD II, ignition misfire will usually set a fault code and turn on the Check Engine light. Fuel that isn't burned causes a huge increase in hydrocarbon emissions and will usually cause a vehicle to fail an emissions test. Unburned fuel also can damage the catalytic converter by causing it to overheat. So if you find a cylinder-specific misfire code such as P0302 (indicating cylinder #2), check the spark plug, plug wire, coil (if it's a DIS or coil-on-plug system), fuel injector and compression to isolate the cause. On the other hand, if you find a random misfire code (P0300), the problem probably is not the ignition system. It's likely a lean fuel mixture caused by a vacuum leak or dirty injectors.
Spark Plug Service
As a rule, replacement spark plugs should have the same or better service interval as the original plugs. Long-life platinum and iridium spark plugs cost a little more than standard spark plugs and are an excellent upgrade for engines that were not originally equipped with these types of plugs. So replace same with same or better - unless an engine that was originally equipped with long-life spark plugs has a plug fouling problem due to high oil consumption. In this case, it doesn't matter what type of spark plugs you install because they won't last as long as normal. If the oil burning problem cannot be fixed, switching to a slightly hotter plug may help reduce fouling.
For performance applications, switching to a slightly cooler spark plug can reduce the risk of pre-ignition and detonation at high rpm and loads.
_____________________________________________
Choosing Racing Spark Plugs
Selecting the proper spark plugs for a performanc engine can mean the difference between front of the pack and a DNF. When using this guide, understand that race plugs are usually of a much colder heat range rating than standard automotive spark plugs. Colder spark plugs must be used in engines with increased cylinder pressures, higher temperatures and greater BHP. Other factors such as fuel delivery (turbo, supercharged), fuel types and piston-to-head clearance will also affect proper plug selection.
Step 1: Shell Design - The first step in choosing the proper race plug is determining the plug type that your cylinder head/piston will accept. Thread diameter and pitch, thread length and shell seat, as well as hex size are all factors that will define what shell type works best for your engine.
Step 2: Electrode Design - The second decision is electrode design and configuration. Is it a fine wire center or standard electrode? Projected or non-projected? Full coverage 'J-Gap' or perhaps a cut-back or angled ground wire? A good rule of thumb is to attain as much projection into the cylinder as possible. But be aware of piston clearance that could prohibit projected spark plugs from being used.
Step 3: Heat Range - The third factor in choosing a race plug is heat range. Correct heat range is critical in maintaining peak performance throughout the duration of your race or event. Switching to a colder or hotter plug will not increase horsepower, but could affect engine performance. Choosing a plug that is too hot can result in preignition or detonation. A plug that is too cold could cause an engine to stumble, misfire or foul.
The main factors to consider in selecting the proper heat range are: type of race, methanol, specific output, nitro-meth, compression ratio, nitrous oxide, horsepower, super or turbo charging and racing fuel.
Courtesy: Champion Spark Plugs
_____________________________________________
Spark Plug Replacement Tips
--Before you install any spark plug, compare the old and new plugs to make sure the replacement spark plugs have the same thread diameter, pitch (SAE or metric), thread length and seat configuration as the original plugs.
--On engines with aluminum heads, let the engine cool before you attempt to loosen and remove the plugs. This will reduce the risk of damaging the threads in the cylinder head.
--Always inspect the old spark plugs after they have been removed and note any conditions that would indicate a cylinder is running rich, lean or is burning oil.
--Spark plug wires should also be inspected - and replaced if the insulation is damaged, if resistance exceeds factory specifications or the boots are loose.
Courtesy NGK Spark Plugs, Inc.
_____________________________________________
Spark Plug Torque and Gap
How much the spark plugs should be tightened depends on the size of the plugs and the type of plug seat. Spark plugs with gasket-style seats require more torque than those with taper seats. Always follow vehicle manufacturer torque recommendations, but as a general rule:
14-mm plugs with a gasket-style seat should be tightened to 26 to 30 ft.-lbs. in cast iron heads, but only 18 to 22 ft.-lbs. in aluminum heads.
18-mm plugs with gasket-style seats should be tightened to 32 to 38 ft.-lbs. in cast iron heads, but only 28 to 34 ft.-lbs. in aluminum heads.
14-mm taper seat spark plugs should be tightened to 7 to 15 ft.-lbs. in both cast iron and aluminum.
18-mm taper seat spark plugs should be tightened to 15 to 20 ft.-lbs. in both types of heads.
As for setting the plug gap, always follow the vehicle manufacturer's recommendations - unless you are installing a set of Bosch's Platinum+4 spark plugs. These plugs are pre-gapped at the factory to a standard 1.6-mm gap. This is necessary to achieve maximum plug performance and longevity, so don't change the gap.
The reason is that the multiple ground electrodes in the Bosch Platinum+4 and Platinum+2 series are made from a special, wear-resistant nickel alloy, enhanced by the addition of yttrium-alloy. Not only do these plugs utilize factory set "surface air gap" technology that doesn't need gapping prior to installation, the manufacturer also said that the special alloys resist erosion so the gap maintains its correct setting for the life of the plug.
"Every time a spark plug fires, a tiny bit of metal is lost in the electrical discharge. Over time, this can degrade a plug's performance," said Otto Stefaner, general product manager, consumer products, for Bosch. "Multiple electrodes and precious metals minimize this degradation from metal transfer."
Stefaner also explained other benefits to their pre-gapped design. "Surface air gap technology also increases the electrode gap for better ignition, without increasing the voltage requirement, enabling the production of a larger flame core in the combustion chamber. Tests show that the four-electrode, platinum-core plugs transfer more energy efficiently to the air/fuel mixture. And plugs with four ground electrodes have up to 33% better cold restart reliability than conventional plugs," he said.
Courtesy Robert Bosch Corp.
Gari.pk User 3334 asked on 02 Jul 2010 18:19:33 pm
3 Answers 
Arham - on 02 Jul 2010 18:19:51 pmdivtext-align: center""Spark Plugs: Do Not Neglect Them
If you had to name one item that has more of an effect on engine performance than anything else, it would have to be the spark plugs. The spark plugs are the business end of the ignition system that deliver the all-important spark needed to ignite the air/fuel mixture. No spark means no combustion, wasted energy, increased emissions, loss of performance, idle roughness, hesitation, hard starting and possibly even a no start if all of the plugs are affected.
Consider for a moment what happens when a plug fires. The spark is created when high voltage supplied by the ignition coil jumps across a small air gap between the plug electrodes. The high voltage surge from the coil goes down the plug center electrode, ionizes the air between the electrodes (the air gap) and forms a spark (arc) as it jumps across the gap to the outer ground electrode. The initial voltage required to form the spark may range from 4,000 up to 28,000 volts depending on the distance between the electrodes, engine load and compression (larger distances, higher engine loads and compression all raise the firing voltage requirements). The spark only lasts about a millisecond, but it is long enough to start the burn.
The instant at which the spark occurs is timed precisely to coincide with the position of the piston as it approaches top dead center on its compression stroke. On most engines, the spark occurs a few degrees before the piston reaches top dead center. If the spark occurs too soon (over advanced timing), cylinder pressures rise too quickly and peak too early in the cycle resulting in a loss of power. This can also cause engine damaging "detonation" (spark knock or ping) to occur. If the spark occurs too late, cylinder pressures peak too late in the cycle also resulting in a loss of power. Timing is controlled by the engine computer and ignition module, not the spark plugs, so a timing problem would indicate a sensor or module problem.
SPARK PLUG PROBLEMS
If an engine cranks but will not start, one of the first things you should check is spark. No spark at any of the plugs usually indicates an ignition problem that requires further investigation (a bad coil, ignition module, distributor pickup, crank sensor, etc.).
If the engine runs but misfires, one or more spark plugs may be worn or fouled, or there may be one or more bad spark plug wires. To diagnose this kind of problem, observe the firing pattern for each cylinder on an oscilloscope. A higher than normal firing voltage in any one cylinder may indicate excessive resistance in a plug wire, a loose plug wire, or a badly worn or misgapped spark plug (too wide). A lower than normal firing voltage in any one cylinder may indicate a shorted plug wire, or a fouled or damaged spark plug.
Fouling is the number one reason why spark plugs have to be replaced. Plugs also have to be replaced for preventive maintenance because the electrodes wear as the plugs age. This increases the distance between the electrodes which in turn leads to a gradual increase in the firing voltage required to jump the gap. The gap on a standard spark plug grows about 0.00063 to 0.000126 inch for every 1,000 miles of normal driving, which means the firing voltage requirements creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually the plugs firing voltage requirements under load exceed the ignition system output resulting in a misfire. But most plugs foul out long before they are worn out.
A single fouled spark plug is bad news because it can kill up to 25% of a four cylinder engines power output. It is like riding a horse with a broken leg. A fouled plug will also cause a big increase in fuel consumption and emissions (more than enough to cause an emissions failure and/or the check engine light to come on if the vehicle has an OBD-II system).
Fouling can occur if fuel or oil deposits build upon the plug electrodes. The ceramic insulator around the center electrode prevents voltage from finding a shortcut to the steel plug shell and ground. Deposits here may form a conductive path for the voltage to bleed off to ground, preventing it from jumping the gap and making a spark. Deposits around the outer ground electrode or between the electrodes may form a barrier or bridge that also prevents a spark from occurring.
Fouling can be a problem if an engine uses oil. Worn valve guide seals and guides can allow oil to be sucked down the guides and into the combustion chamber. A heavy buildup of thick black deposits on the plug and intake valve would indicate such a problem. Worn or broken rings, or damage to the cylinder wall can also allow oil to enter the combustion chamber and form ash deposits on the plugs.
Extensive idling and/or short trip stop and go driving can also lead to a rapid buildup of normal fuel deposits. This occurs because the plugs never get hot enough to burn off the deposits, something which plugs are designed to do.
Powdery black deposits on the plugs can occur from "carbon fouling." The underlying cause here is a rich fuel mixture. On an older carbureted engine, the problem might be a broken or stuck choke. On a fuel injected engine, the problem might be a leaky injector, or a dead oxygen sensor or coolant sensor that prevents the engine control system from going into closed loop and leaning out the fuel mixture.
"Reading" the old plugs can reveal not only the cause of a fouling problem but other types of engine problems too such as preignition and detonation. A melted or badly eroded electrode may be the result of overadvanced ignition timing, engine overheating, low octane fuel, or too hot a plug for the application.
SPARK PLUG HEAT RANGE
The "heat range" of a spark plug determines how hot the plug runs during normal operation. If the heat range is correctly matched to the engine application, the plug will run hot enough under normal driving conditions to burn off fouling deposits before they can cause problems. Likewise, the plug will not get too hot and become a source of ignition causing engine-damaging preignition and detonation. If the heat range is too cool for the application, though, fouling deposits may build up faster than they are burned off.
For this reason, always follow the vehicle manufacturer or plug supplier heat range recommendations when selecting a spark plug for a particular application. Two spark plugs may appear to be identical on the outside but have entirely different heat ranges.
There are situations, though, that may require a slightly hotter or colder plug than the one normally recommended. Switching to a slightly hotter plug can help reduce fouling in an older engine that uses oil, for an engine that spends a lot of time idling or is used for short trip stop-and-go driving. But a hotter plug should not be used unless an engine is experiencing a fouling problem because of the increased risk of preignition and detonation.
For performance applications (racing, or engines that are run under heavier than normal loads or at high rpm for sustained periods of time), switching to a slightly colder plug can minimize the risk of preignition and detonation. Even so, a colder plug can increase the risk of fouling with extended idling and low speed operation.
Many of today�s spark plugs have a very broad heat range because the plug manufacturer uses a copper core or platinum center electrode. Copper is an excellent conductor of heat, so the insulator can be designed to run hotter and burn off fouling deposits without it getting too hot under increased load to cause preignition or detonation. A solid platinum center electrode will also carry heat away from the tip, but not if the electrode only has a platinum tip.
SPARK PLUG REPLACEMENT OPTIONS
The recommended replacement interval for standard spark plugs has typically been every 30,000 to 45,000 miles. But most of extended life plugs have special wear-resistant electrodes made of platinum, iridium, nickel yttrium or other exotic alloys that minimize electrode erosion. Such plugs can usually go 100,000 miles plus with little or no electrode wear. Even so, they may still be vulnerable to fouling if an engine has an oil consumption problem or spends excessive amounts of time idling.
Extended life spark plugs are a good upgrade for many engines, but may not be the best choice for an older engine that uses oil or even some performance engines.
According to one plug manufacturer, platinum tipped electrodes run hotter than standard electrodes. This may increase the risk of preignition and detonation in some turbocharged and high performance engines. For such applications, a standard plug with a colder heat range might be a safer choice.
There are also a wide variety of electrode configurations from which to choose today. Each manufacturer claims certain performance benefits for their particular design. It may be reduced electrode wear, or improved ignition reliability, or both. Such plugs are often marketed as "premium" or "performance" plugs, and may command a price of up to $6 or $7 apiece.
Some of these plugs (as well as standard plugs) also have multiple electrodes (two, three or four ground electrodes). A spark plugs with more than one ground electrode will still only produce one spark per ignition cycle. But with four paths from which to choose, the likelihood of getting a good spark to at least one of the ground electrodes is multiplied for improved ignition reliability. Having more than one ground electrode also distributes the wear to minimize electrode erosion and growth of the spark gap over time. Some such plugs also experience a self-cleaning effect because the sideways path of the spark helps burn deposits off of the insulator.
Are premium plugs worth the extra money? They are if they can provide extended plug life, reduce the need for maintenance or improve overall ignition performance. The plugs in many front-wheel drive cars and minivans with V6 engines are very difficult to replace. Installing extended life plugs can almost eliminate the plug change hassle for good. Likewise, performance plugs that reduce misfires can enhance performance for a smoother running, cleaner more fuel efficient engine. No spark plug can create power out of thin air, but improved ignition reliability can minimize any horsepower loss due to misfire.
When the spark plugs are changed, they should not be removed on engines with aluminum cylinder heads until the engine has cooled. This will minimize the risk of damaging the threads in the head when the plugs come out.
Most threads on spark plugs designed for aluminum head applications are precoated to reduce the risk of thread damage. If you are in the habit of applying a drop of antiseize compound to the plug threads before they go in for added insurance, you might want to reconsider this practice. One vehicle manufacturer warns against this practice because antiseize acts like a lubricant and may allow the plugs to be overtightened, which can damage the threads. Their advice is to reduce the tightening torque on the plugs 40% if you decide to use antiseize on the threads.
TIGHTENING SPARK PLUGS: BE CAREFUL!
How much the spark plugs should be tightened depends on the size of the plugs and the type of plug seat. Spark plugs with gasket style seats require more torque than those with taper seats.
Always follow the vehicle manufacturer torque recommendations, but as a general rule 14 mm plugs with a gasket style seat should be tightened to 26 to 30 ft.lbs. in cast iron heads, but only 18 to 22 ft.lbs. in aluminum heads. Likewise, 18 mm plugs with gasket style seats should be tightened to 32 to 38 ft.lbs. in cast iron heads but only 28 to 34 ft.lbs. in aluminum heads. For taper seat spark plugs, 14 mm plugs should be tightened to 7 to 15 ft.lbs. in both cast iron and aluminum, while 18 mm taper seat plugs should be tightened to 15 to 20 ft.lbs. in both types of heads.
SPARK PLUG GAP
As for setting the plug gap, always follow the vehicle manufacturer recommendations. Spark plug gaps typically range from .028 inches up to .034 inches or even larger. One exception here is Bosch Platinum+4 or Platinum+2 spark plugs. These plugs are pregapped at the factory to a standard 1.6 mm gap and should NOT be altered regardless of what the vehicle manufacturer spacifies for the engine. Bosch says this is necessary to achieve maximum plug performance and longevity, so do not change the gap.
Finally, play close attention to the condition of the spark plug cables and boots when changing the plugs. Loose fitting boots or damaged cables can cause ignition misfire. Also, make sure the cables are properly routed and suppored in their looms to avoid crossfire problems and contact with the hot exhaust manifold.
If you had to name one item that has more of an effect on engine performance than anything else, it would have to be the spark plugs. The spark plugs are the business end of the ignition system that deliver the all-important spark needed to ignite the air/fuel mixture. No spark means no combustion, wasted energy, increased emissions, loss of performance, idle roughness, hesitation, hard starting and possibly even a no start if all of the plugs are affected.
Consider for a moment what happens when a plug fires. The spark is created when high voltage supplied by the ignition coil jumps across a small air gap between the plug electrodes. The high voltage surge from the coil goes down the plug center electrode, ionizes the air between the electrodes (the air gap) and forms a spark (arc) as it jumps across the gap to the outer ground electrode. The initial voltage required to form the spark may range from 4,000 up to 28,000 volts depending on the distance between the electrodes, engine load and compression (larger distances, higher engine loads and compression all raise the firing voltage requirements). The spark only lasts about a millisecond, but it is long enough to start the burn.
The instant at which the spark occurs is timed precisely to coincide with the position of the piston as it approaches top dead center on its compression stroke. On most engines, the spark occurs a few degrees before the piston reaches top dead center. If the spark occurs too soon (over advanced timing), cylinder pressures rise too quickly and peak too early in the cycle resulting in a loss of power. This can also cause engine damaging "detonation" (spark knock or ping) to occur. If the spark occurs too late, cylinder pressures peak too late in the cycle also resulting in a loss of power. Timing is controlled by the engine computer and ignition module, not the spark plugs, so a timing problem would indicate a sensor or module problem.
SPARK PLUG PROBLEMS
If an engine cranks but will not start, one of the first things you should check is spark. No spark at any of the plugs usually indicates an ignition problem that requires further investigation (a bad coil, ignition module, distributor pickup, crank sensor, etc.).
If the engine runs but misfires, one or more spark plugs may be worn or fouled, or there may be one or more bad spark plug wires. To diagnose this kind of problem, observe the firing pattern for each cylinder on an oscilloscope. A higher than normal firing voltage in any one cylinder may indicate excessive resistance in a plug wire, a loose plug wire, or a badly worn or misgapped spark plug (too wide). A lower than normal firing voltage in any one cylinder may indicate a shorted plug wire, or a fouled or damaged spark plug.
Fouling is the number one reason why spark plugs have to be replaced. Plugs also have to be replaced for preventive maintenance because the electrodes wear as the plugs age. This increases the distance between the electrodes which in turn leads to a gradual increase in the firing voltage required to jump the gap. The gap on a standard spark plug grows about 0.00063 to 0.000126 inch for every 1,000 miles of normal driving, which means the firing voltage requirements creep up about 500 volts for every 10,000 to 15,000 miles of driving. Eventually the plugs firing voltage requirements under load exceed the ignition system output resulting in a misfire. But most plugs foul out long before they are worn out.
A single fouled spark plug is bad news because it can kill up to 25% of a four cylinder engines power output. It is like riding a horse with a broken leg. A fouled plug will also cause a big increase in fuel consumption and emissions (more than enough to cause an emissions failure and/or the check engine light to come on if the vehicle has an OBD-II system).
Fouling can occur if fuel or oil deposits build upon the plug electrodes. The ceramic insulator around the center electrode prevents voltage from finding a shortcut to the steel plug shell and ground. Deposits here may form a conductive path for the voltage to bleed off to ground, preventing it from jumping the gap and making a spark. Deposits around the outer ground electrode or between the electrodes may form a barrier or bridge that also prevents a spark from occurring.
Fouling can be a problem if an engine uses oil. Worn valve guide seals and guides can allow oil to be sucked down the guides and into the combustion chamber. A heavy buildup of thick black deposits on the plug and intake valve would indicate such a problem. Worn or broken rings, or damage to the cylinder wall can also allow oil to enter the combustion chamber and form ash deposits on the plugs.
Extensive idling and/or short trip stop and go driving can also lead to a rapid buildup of normal fuel deposits. This occurs because the plugs never get hot enough to burn off the deposits, something which plugs are designed to do.
Powdery black deposits on the plugs can occur from "carbon fouling." The underlying cause here is a rich fuel mixture. On an older carbureted engine, the problem might be a broken or stuck choke. On a fuel injected engine, the problem might be a leaky injector, or a dead oxygen sensor or coolant sensor that prevents the engine control system from going into closed loop and leaning out the fuel mixture.
"Reading" the old plugs can reveal not only the cause of a fouling problem but other types of engine problems too such as preignition and detonation. A melted or badly eroded electrode may be the result of overadvanced ignition timing, engine overheating, low octane fuel, or too hot a plug for the application.
SPARK PLUG HEAT RANGE
The "heat range" of a spark plug determines how hot the plug runs during normal operation. If the heat range is correctly matched to the engine application, the plug will run hot enough under normal driving conditions to burn off fouling deposits before they can cause problems. Likewise, the plug will not get too hot and become a source of ignition causing engine-damaging preignition and detonation. If the heat range is too cool for the application, though, fouling deposits may build up faster than they are burned off.
For this reason, always follow the vehicle manufacturer or plug supplier heat range recommendations when selecting a spark plug for a particular application. Two spark plugs may appear to be identical on the outside but have entirely different heat ranges.
There are situations, though, that may require a slightly hotter or colder plug than the one normally recommended. Switching to a slightly hotter plug can help reduce fouling in an older engine that uses oil, for an engine that spends a lot of time idling or is used for short trip stop-and-go driving. But a hotter plug should not be used unless an engine is experiencing a fouling problem because of the increased risk of preignition and detonation.
For performance applications (racing, or engines that are run under heavier than normal loads or at high rpm for sustained periods of time), switching to a slightly colder plug can minimize the risk of preignition and detonation. Even so, a colder plug can increase the risk of fouling with extended idling and low speed operation.
Many of today�s spark plugs have a very broad heat range because the plug manufacturer uses a copper core or platinum center electrode. Copper is an excellent conductor of heat, so the insulator can be designed to run hotter and burn off fouling deposits without it getting too hot under increased load to cause preignition or detonation. A solid platinum center electrode will also carry heat away from the tip, but not if the electrode only has a platinum tip.
SPARK PLUG REPLACEMENT OPTIONS
The recommended replacement interval for standard spark plugs has typically been every 30,000 to 45,000 miles. But most of extended life plugs have special wear-resistant electrodes made of platinum, iridium, nickel yttrium or other exotic alloys that minimize electrode erosion. Such plugs can usually go 100,000 miles plus with little or no electrode wear. Even so, they may still be vulnerable to fouling if an engine has an oil consumption problem or spends excessive amounts of time idling.
Extended life spark plugs are a good upgrade for many engines, but may not be the best choice for an older engine that uses oil or even some performance engines.
According to one plug manufacturer, platinum tipped electrodes run hotter than standard electrodes. This may increase the risk of preignition and detonation in some turbocharged and high performance engines. For such applications, a standard plug with a colder heat range might be a safer choice.
There are also a wide variety of electrode configurations from which to choose today. Each manufacturer claims certain performance benefits for their particular design. It may be reduced electrode wear, or improved ignition reliability, or both. Such plugs are often marketed as "premium" or "performance" plugs, and may command a price of up to $6 or $7 apiece.
Some of these plugs (as well as standard plugs) also have multiple electrodes (two, three or four ground electrodes). A spark plugs with more than one ground electrode will still only produce one spark per ignition cycle. But with four paths from which to choose, the likelihood of getting a good spark to at least one of the ground electrodes is multiplied for improved ignition reliability. Having more than one ground electrode also distributes the wear to minimize electrode erosion and growth of the spark gap over time. Some such plugs also experience a self-cleaning effect because the sideways path of the spark helps burn deposits off of the insulator.
Are premium plugs worth the extra money? They are if they can provide extended plug life, reduce the need for maintenance or improve overall ignition performance. The plugs in many front-wheel drive cars and minivans with V6 engines are very difficult to replace. Installing extended life plugs can almost eliminate the plug change hassle for good. Likewise, performance plugs that reduce misfires can enhance performance for a smoother running, cleaner more fuel efficient engine. No spark plug can create power out of thin air, but improved ignition reliability can minimize any horsepower loss due to misfire.
When the spark plugs are changed, they should not be removed on engines with aluminum cylinder heads until the engine has cooled. This will minimize the risk of damaging the threads in the head when the plugs come out.
Most threads on spark plugs designed for aluminum head applications are precoated to reduce the risk of thread damage. If you are in the habit of applying a drop of antiseize compound to the plug threads before they go in for added insurance, you might want to reconsider this practice. One vehicle manufacturer warns against this practice because antiseize acts like a lubricant and may allow the plugs to be overtightened, which can damage the threads. Their advice is to reduce the tightening torque on the plugs 40% if you decide to use antiseize on the threads.
TIGHTENING SPARK PLUGS: BE CAREFUL!
How much the spark plugs should be tightened depends on the size of the plugs and the type of plug seat. Spark plugs with gasket style seats require more torque than those with taper seats.
Always follow the vehicle manufacturer torque recommendations, but as a general rule 14 mm plugs with a gasket style seat should be tightened to 26 to 30 ft.lbs. in cast iron heads, but only 18 to 22 ft.lbs. in aluminum heads. Likewise, 18 mm plugs with gasket style seats should be tightened to 32 to 38 ft.lbs. in cast iron heads but only 28 to 34 ft.lbs. in aluminum heads. For taper seat spark plugs, 14 mm plugs should be tightened to 7 to 15 ft.lbs. in both cast iron and aluminum, while 18 mm taper seat plugs should be tightened to 15 to 20 ft.lbs. in both types of heads.
SPARK PLUG GAP
As for setting the plug gap, always follow the vehicle manufacturer recommendations. Spark plug gaps typically range from .028 inches up to .034 inches or even larger. One exception here is Bosch Platinum+4 or Platinum+2 spark plugs. These plugs are pregapped at the factory to a standard 1.6 mm gap and should NOT be altered regardless of what the vehicle manufacturer spacifies for the engine. Bosch says this is necessary to achieve maximum plug performance and longevity, so do not change the gap.
Finally, play close attention to the condition of the spark plug cables and boots when changing the plugs. Loose fitting boots or damaged cables can cause ignition misfire. Also, make sure the cables are properly routed and suppored in their looms to avoid crossfire problems and contact with the hot exhaust manifold.
Konain - on 02 Jul 2010 18:20:12 pmdivtext-align: center""Spark Plugs: Why They Still Need To Be Replaced
One of the leading causes of hard starting is fouled or worn spark plugs. When a fuel injected engine that normally starts quite easily has to be coaxed to life, it often means the spark plugs are overdue for a change. As the electrodes wear, the voltage required to jump the gap and ignite the fuel mixture goes up. At the same time, accumulated deposits on the insulator can drain off voltage before it even has a chance to form a spark. So the engine fails to start or starts only reluctantly after prolonged cranking.
One of the reasons why spark plug sales take off when cold weather arrives is because many motorists put off changing the plugs until they absolutely have to. The spark plugs continue to rack up mile after mile until they have deteriorated to the point where they are causing noticeable starting and driveability problems.
Emission checks will catch a lot of bad spark plugs and force motorists to change plugs that need to be replaced. But in areas where emission checks are not required, the only incentives for changing the spark plugs are the driveability problems created by the plugs themselves. So many motorists today think they are saving money on maintenance by putting off a spark plug change until it is obvious the engine needs new spark plugs. Then and only then will they begrudgingly spend any money on a new set of spark plugs.
WHY CHANGE THE SPARK PLUGS?
What motorists need to know is that spark plugs do NOT last forever, even the long-life 100,000 mile plugs. All spark plugs need to be changed sooner or later. Here's why:
REASON #1: New plugs maintain peak engine performance and efficiency. Every engine will misfire occasionally. But as the number of misfires per mile goes up over time, it increases exhaust emissions, wastes gas and reduces power. In the past, most motorist would not notice the gradual decline in ignition performance until it reached a point where it created a steady miss, caused the engine to run rough, buck or stall, or made it hard to start. Not so today. All 1996 and newer vehicles have an OBD II onboard diagnostic system that tracks ignition misfires. When the rate of misfires exceeds a certain limit and causes emissions to increase 50% over baseline levels, it illuminates a warning light. Too bad older vehicle do not have this watchdog system. So on older vehicles, replacing the spark plugs at the recommended service intervals for preventive maintenance will reduce the risk of misfires and maintain peak engine performance. For standard spark plugs, the service interval is typically every 45,000 miles. For platinum spark plugs, it is 100,000 miles.
A new set of plugs is not a cure-all for driveability and emissions problems, but in many cases a plug change can make a significant improvement. Changing the plugs can reduce hydrocarbon (HC) emissions up to several hundred parts per million, which may make the difference between failing and passing an emissions test.
REASON #2: New plugs improve cold starting. Bad plugs are often responsible for many cold weather "no start" service calls. Many times the battery has been run dead while cranking the engine because the plugs would not light the fire. When the old plugs are removed and examined, they are often found to be worn or dirty. New plugs reduce the voltage requirements on the ignition system, which decreases the chance of misfire while leaving more amps for the starter and injectors.
Wet fouled plugs can also prevent an engine from starting, but in many instances the fouling problem has nothing to do with plug wear or neglect. If an engine is flooded with fuel while it is being cranked, gasoline can soak the plugs and bleed off the ignition voltage before it forms a spark. Wet fouling tends to be more common on older vehicles that have carburetors because pumping the gas pedal can easily flood the engine with too much fuel. Flooding can also occur if the choke sticks, the float is set too high or the needle valve leaks. On fuel injected engines, wet fouling is less of a problem but can happen if a cold start injector leaks or there is a fuel calibration problem that creates an overly rich startup mixture. The cure in all cases is to wait for the plugs to dry out, or to remove the plugs and clean or replace them.
REASON #3: New plugs minimize the risk of catalytic converter failure. A single misfiring plug can dump enough raw fuel into the exhaust to overheat and damage the converter. The presence of higher than normal quantities of unburned gasoline in the exhaust will cause the operating temperature of the converter to soar, which may lead to a partial of complete meltdown of the converter substrate. This, in turn, may form a partial restriction or complete blockage in the exhaust that creates enormous backpressure and chokes off the engines ability to exhale. The engine may lack power, especially at higher speeds, and deliver terrible fuel economy. Or, it may stall and refuse to run after it is first started. Replacing the converter will solve the restriction problem. But unless the spark plugs are replaced, the new converter may soon die from the same ailment.
ABOUT SPARK PLUGS
The spark plugs are the business end of the ignition system. Whether an engine has a conventional distributor or a direct ignition (distributorless) system, a good set of plugs is absolutely essential for peak performance.
The typical spark plug needs anywhere from 5,000 to 25,000 volts from the ignition coil before it will fire. The exact firing voltage depends on:
Plug gap
The wider the gap, the higher the voltage required. The gap must be set to specs for good ignition performance.
Electrode condition
Wear increase voltage requirements.
Engine load
Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
Resistance
Electrical resistance in the plugs and wires increases voltage required. Replacing worn, damaged or loose fitting plug wires is recommended for improving ignition reliability.
Operating temperature
A cold plug requires more voltage to fire than a hot one.
Reliable ignition, therefore, requires a hot spark from the coil, good plug wires to carry the juice, and spark plugs that are clean, in good condition and gapped properly. If any of these criteria are not met, the spark may not reach it intended destination causing the engine to misfire.
One way to tell if the plugs need changing is to look at a vehicle's odometer. If it has been more than the recommended number of miles (usually 30,000) since the spark plugs were last changed, it is time for a new set.
Another way to tell is to observe the secondary ignition pattern on an oscilloscope. If there is an open plug or wire, the plug will not fire causing the firing voltage to shoot up to the maximum output of the coil. Badly worn plugs or plugs that have been misgapped too wide will also increase the firing voltage dramatically (as can a bad rotor and/or ignition cables with excessive resistance). If the required voltage exceeds the maximum output of the system, the plugs may not fire. If the pattern shows initial secondary spikes approaching the upper voltage limits of the system, therefore, it is a sure sign that the plugs (and/or cap, rotor and cables) need attention.
A fouled plug (or shored ignition cable), on the other hand, will show an unusually low firing voltage.
Firing voltages should not vary by more than 3 kV cylinder to cylinder. A cylinder that shows an abnormally low firing voltage probably has a grounded spark plug (deposits bridging the electrode gap), or a shorted ignition cable. A cylinder that shows an abnormally high firing voltage compared to the others likely has an open ignition cable or a plug with a wide gap.
The plug firing time (spark firing line) portion of the secondary ignition display shows the duration of the spark in milliseconds (thousandths of a second). The average spark duration with the engine idling should be about 1.5 milliseconds.
A duration of less than 0.8 milliseconds would mean there either is not enough voltage to keep the spark going (low coil output), or the voltage is having trouble reaching its destination (excessive resistance in the plug wires).
A longer than normal spark (1.8 milliseconds or more) is an indication that the firing voltage is experiencing little resistance because a plug is fouled or grounded (or a plug wire is shorted) probably due to accumulated carbon deposits. Fouling can be a problem if a plug's heat range is too cold for the application (which can be solved by installing hotter plugs). But it may also be the result of excessive oil consumption due to worn valve guides or seals, worn rings, or even short trip stop-and-go driving.
Intermittent misfires can be caused by a variety of ignition, fuel or mechanical problems. Lean misfire occurs when there is too much air and not enough fuel, so the engine should be checked for air or vacuum leaks, dirty injectors, carburetion problems or a leaky EGR valve. If the misfire appears to "jump around" from cylinder to cylinder, a manifold vacuum leak or a leaky EGR valve may be the cause. But if the misfire is isolated to a single cylinder, a worn or fouled spark plug (or bad plug wire) is the most likely cause.
One of the leading causes of hard starting is fouled or worn spark plugs. When a fuel injected engine that normally starts quite easily has to be coaxed to life, it often means the spark plugs are overdue for a change. As the electrodes wear, the voltage required to jump the gap and ignite the fuel mixture goes up. At the same time, accumulated deposits on the insulator can drain off voltage before it even has a chance to form a spark. So the engine fails to start or starts only reluctantly after prolonged cranking.
One of the reasons why spark plug sales take off when cold weather arrives is because many motorists put off changing the plugs until they absolutely have to. The spark plugs continue to rack up mile after mile until they have deteriorated to the point where they are causing noticeable starting and driveability problems.
Emission checks will catch a lot of bad spark plugs and force motorists to change plugs that need to be replaced. But in areas where emission checks are not required, the only incentives for changing the spark plugs are the driveability problems created by the plugs themselves. So many motorists today think they are saving money on maintenance by putting off a spark plug change until it is obvious the engine needs new spark plugs. Then and only then will they begrudgingly spend any money on a new set of spark plugs.
WHY CHANGE THE SPARK PLUGS?
What motorists need to know is that spark plugs do NOT last forever, even the long-life 100,000 mile plugs. All spark plugs need to be changed sooner or later. Here's why:
REASON #1: New plugs maintain peak engine performance and efficiency. Every engine will misfire occasionally. But as the number of misfires per mile goes up over time, it increases exhaust emissions, wastes gas and reduces power. In the past, most motorist would not notice the gradual decline in ignition performance until it reached a point where it created a steady miss, caused the engine to run rough, buck or stall, or made it hard to start. Not so today. All 1996 and newer vehicles have an OBD II onboard diagnostic system that tracks ignition misfires. When the rate of misfires exceeds a certain limit and causes emissions to increase 50% over baseline levels, it illuminates a warning light. Too bad older vehicle do not have this watchdog system. So on older vehicles, replacing the spark plugs at the recommended service intervals for preventive maintenance will reduce the risk of misfires and maintain peak engine performance. For standard spark plugs, the service interval is typically every 45,000 miles. For platinum spark plugs, it is 100,000 miles.
A new set of plugs is not a cure-all for driveability and emissions problems, but in many cases a plug change can make a significant improvement. Changing the plugs can reduce hydrocarbon (HC) emissions up to several hundred parts per million, which may make the difference between failing and passing an emissions test.
REASON #2: New plugs improve cold starting. Bad plugs are often responsible for many cold weather "no start" service calls. Many times the battery has been run dead while cranking the engine because the plugs would not light the fire. When the old plugs are removed and examined, they are often found to be worn or dirty. New plugs reduce the voltage requirements on the ignition system, which decreases the chance of misfire while leaving more amps for the starter and injectors.
Wet fouled plugs can also prevent an engine from starting, but in many instances the fouling problem has nothing to do with plug wear or neglect. If an engine is flooded with fuel while it is being cranked, gasoline can soak the plugs and bleed off the ignition voltage before it forms a spark. Wet fouling tends to be more common on older vehicles that have carburetors because pumping the gas pedal can easily flood the engine with too much fuel. Flooding can also occur if the choke sticks, the float is set too high or the needle valve leaks. On fuel injected engines, wet fouling is less of a problem but can happen if a cold start injector leaks or there is a fuel calibration problem that creates an overly rich startup mixture. The cure in all cases is to wait for the plugs to dry out, or to remove the plugs and clean or replace them.
REASON #3: New plugs minimize the risk of catalytic converter failure. A single misfiring plug can dump enough raw fuel into the exhaust to overheat and damage the converter. The presence of higher than normal quantities of unburned gasoline in the exhaust will cause the operating temperature of the converter to soar, which may lead to a partial of complete meltdown of the converter substrate. This, in turn, may form a partial restriction or complete blockage in the exhaust that creates enormous backpressure and chokes off the engines ability to exhale. The engine may lack power, especially at higher speeds, and deliver terrible fuel economy. Or, it may stall and refuse to run after it is first started. Replacing the converter will solve the restriction problem. But unless the spark plugs are replaced, the new converter may soon die from the same ailment.
ABOUT SPARK PLUGS
The spark plugs are the business end of the ignition system. Whether an engine has a conventional distributor or a direct ignition (distributorless) system, a good set of plugs is absolutely essential for peak performance.
The typical spark plug needs anywhere from 5,000 to 25,000 volts from the ignition coil before it will fire. The exact firing voltage depends on:
Plug gap
The wider the gap, the higher the voltage required. The gap must be set to specs for good ignition performance.
Electrode condition
Wear increase voltage requirements.
Engine load
Higher load increases voltage needed. If the plugs are worn or gapped to wide, they may misfire under load.
Resistance
Electrical resistance in the plugs and wires increases voltage required. Replacing worn, damaged or loose fitting plug wires is recommended for improving ignition reliability.
Operating temperature
A cold plug requires more voltage to fire than a hot one.
Reliable ignition, therefore, requires a hot spark from the coil, good plug wires to carry the juice, and spark plugs that are clean, in good condition and gapped properly. If any of these criteria are not met, the spark may not reach it intended destination causing the engine to misfire.
One way to tell if the plugs need changing is to look at a vehicle's odometer. If it has been more than the recommended number of miles (usually 30,000) since the spark plugs were last changed, it is time for a new set.
Another way to tell is to observe the secondary ignition pattern on an oscilloscope. If there is an open plug or wire, the plug will not fire causing the firing voltage to shoot up to the maximum output of the coil. Badly worn plugs or plugs that have been misgapped too wide will also increase the firing voltage dramatically (as can a bad rotor and/or ignition cables with excessive resistance). If the required voltage exceeds the maximum output of the system, the plugs may not fire. If the pattern shows initial secondary spikes approaching the upper voltage limits of the system, therefore, it is a sure sign that the plugs (and/or cap, rotor and cables) need attention.
A fouled plug (or shored ignition cable), on the other hand, will show an unusually low firing voltage.
Firing voltages should not vary by more than 3 kV cylinder to cylinder. A cylinder that shows an abnormally low firing voltage probably has a grounded spark plug (deposits bridging the electrode gap), or a shorted ignition cable. A cylinder that shows an abnormally high firing voltage compared to the others likely has an open ignition cable or a plug with a wide gap.
The plug firing time (spark firing line) portion of the secondary ignition display shows the duration of the spark in milliseconds (thousandths of a second). The average spark duration with the engine idling should be about 1.5 milliseconds.
A duration of less than 0.8 milliseconds would mean there either is not enough voltage to keep the spark going (low coil output), or the voltage is having trouble reaching its destination (excessive resistance in the plug wires).
A longer than normal spark (1.8 milliseconds or more) is an indication that the firing voltage is experiencing little resistance because a plug is fouled or grounded (or a plug wire is shorted) probably due to accumulated carbon deposits. Fouling can be a problem if a plug's heat range is too cold for the application (which can be solved by installing hotter plugs). But it may also be the result of excessive oil consumption due to worn valve guides or seals, worn rings, or even short trip stop-and-go driving.
Intermittent misfires can be caused by a variety of ignition, fuel or mechanical problems. Lean misfire occurs when there is too much air and not enough fuel, so the engine should be checked for air or vacuum leaks, dirty injectors, carburetion problems or a leaky EGR valve. If the misfire appears to "jump around" from cylinder to cylinder, a manifold vacuum leak or a leaky EGR valve may be the cause. But if the misfire is isolated to a single cylinder, a worn or fouled spark plug (or bad plug wire) is the most likely cause.
Zubair - on 02 Jul 2010 18:20:36 pmREADING SPARK PLUGS
Examining the tips of the spark plugs as they are removed can reveal a great deal about the health and performance of an engine. The appearance and color of the deposits can reveal other problems that may need fixing:
Normal deposits
Light brown or tan colored.
Fuel fouled spark plug
Black fluffy carbon deposits indicate an overly rich fuel mixture or possibly a weak spark. Check for such things as a stuck choke, a heavy or misadjusted carburetor float, a leaky needle valve in the carburetor, leaky injectors, low coil output or high resistance in the plug wires.
Wet spark plug
A wet spark plug means the plug has not been firing. If not due to engine flooding, the problem may be a bad ignition cable (excessive resistance, shorted or arcing). But wet fouling can also be caused by dirt or moisture on the outside of the plug that provides a conductive path to ground, or by an internal crack in the ceramic insulator that shorts the plug to ground.
Oil fouled spark plug
Heavy black deposits with an oily appearance. These are the result of oil entering in the combustion chamber, probably past worn valve guides, guide seals or rings. Switching to a hotter plug may help prolong plug life somewhat, but no spark plug will survive long under such conditions. The only permanent cure to this condition is to fix the oil consumption problem.
Glazed spark plug
Yellowish melted appearing deposits on the insulator tip that result from high temperature operation. The engine may be running too hot (check for cooling problems), the EGR valve may be inoperative and/or the heat range of the plug may be too hot for the application. Switching to a cooler plug may be necessary if no other problems are found.
Damaged plug
If the electrodes have been smashed flat or broken, somebody put the wrong plug in the engine. A plug that protrudes too far into the combustion chamber may hit the piston or a valve. Always follow the plug manufacturers application recommendations when selecting replacement plugs to prevent this kind of problem.
Overheating
If the spark plug insulator is blistered, white and free from deposits, something is making the plug run too hot. If the heat range is not too hot for the application, check for cooling problems, incorrect ignition timing or a lean fuel mixture.
Melted electrode
A symptom of severe preignition. The spark plug has been running too hot for a long time (see overheating above). This can be very damaging and may burn a hole through the top of a piston!
Detonation
If the insulator is split or chipped, detonation (spark knock) may be occurring in the engine. The underlying cause here might be an inoperative EGR valve, overadvanced ignition timing, excessive compression due to accumulated deposits in the combustion chamber, or engine overheating.
Examining the tips of the spark plugs as they are removed can reveal a great deal about the health and performance of an engine. The appearance and color of the deposits can reveal other problems that may need fixing:
Normal deposits
Light brown or tan colored.
Fuel fouled spark plug
Black fluffy carbon deposits indicate an overly rich fuel mixture or possibly a weak spark. Check for such things as a stuck choke, a heavy or misadjusted carburetor float, a leaky needle valve in the carburetor, leaky injectors, low coil output or high resistance in the plug wires.
Wet spark plug
A wet spark plug means the plug has not been firing. If not due to engine flooding, the problem may be a bad ignition cable (excessive resistance, shorted or arcing). But wet fouling can also be caused by dirt or moisture on the outside of the plug that provides a conductive path to ground, or by an internal crack in the ceramic insulator that shorts the plug to ground.
Oil fouled spark plug
Heavy black deposits with an oily appearance. These are the result of oil entering in the combustion chamber, probably past worn valve guides, guide seals or rings. Switching to a hotter plug may help prolong plug life somewhat, but no spark plug will survive long under such conditions. The only permanent cure to this condition is to fix the oil consumption problem.
Glazed spark plug
Yellowish melted appearing deposits on the insulator tip that result from high temperature operation. The engine may be running too hot (check for cooling problems), the EGR valve may be inoperative and/or the heat range of the plug may be too hot for the application. Switching to a cooler plug may be necessary if no other problems are found.
Damaged plug
If the electrodes have been smashed flat or broken, somebody put the wrong plug in the engine. A plug that protrudes too far into the combustion chamber may hit the piston or a valve. Always follow the plug manufacturers application recommendations when selecting replacement plugs to prevent this kind of problem.
Overheating
If the spark plug insulator is blistered, white and free from deposits, something is making the plug run too hot. If the heat range is not too hot for the application, check for cooling problems, incorrect ignition timing or a lean fuel mixture.
Melted electrode
A symptom of severe preignition. The spark plug has been running too hot for a long time (see overheating above). This can be very damaging and may burn a hole through the top of a piston!
Detonation
If the insulator is split or chipped, detonation (spark knock) may be occurring in the engine. The underlying cause here might be an inoperative EGR valve, overadvanced ignition timing, excessive compression due to accumulated deposits in the combustion chamber, or engine overheating.
User Also Viewed
Spark Plugs: All The Details You Need To Know
My Ads |
Messages |
Blog |
Forum |
Petrol Prices |
Fuel Cost Calculator
Close x
Sell Online
- Sell Your Car
- Sell Your Bike
- Sell Your Commercial Vehicle
- Sell Your Accessory
- Car Price Offers
- Car Insurance
Gari VIP
- Car Forum
- Automotive News
- Auto Video Channel
- Online Vehicle Verification
- Petrol Prices in Pakistan
- Fuel Prices in Pakistan
- Fuel Cost Calculator
- Driving License Test
- Gari Rides
- sitemap
Gari.pk گاڑی
Copyright © 2024 - 2025 Gari.pk | Car Prices in Pakistan | Gari | گاڑی | Terms & Conditions | Privacy Policy | Car for Sale | Bike for Sale | Commercial Vehicle for Sale
Gari for Cheap cars, Japanese cars, low price, small & big cars, EV, Jeeps, vintage Cars & bikes, bus, truck, tractor, rickshaw sale and purchase on installment or lease.
Gari for Cheap cars, Japanese cars, low price, small & big cars, EV, Jeeps, vintage Cars & bikes, bus, truck, tractor, rickshaw sale and purchase on installment or lease.