Prosmatic Poor Economy Issue Finally Solved

Dear All,

I own a 2002 Vti orial Prosmatic for last 3 years. It was preinstalled with CNG kit. Its fuel consumption (both on petrol and CNG) had been way too much. This is how it was :
CNG= 160 Highway/ 100 City (W/O A/C) (60 liters tank)
Petrol= 13 KM/L Highway / 7.5 City

A lot of diagnostics and visits to Honda 3S didnt help at all. Honda even advised me that this is best I would get from this car. But I was never satisfied as a cousin of mine with same car regularly gets 10+ Km/l within Karachi city. I finally took control of my diagnostics and found following symptoms:

1. The problem is worst is winters. Summers are better.
2. Takes way too long to warmup especially in winters.
3. The torque converter never locks within city
4. On highways, the torque converter locks for a couple of minutes after a stopover but after that automatically unlocks and remains so untill the next stopover.
5. The radiator fan never turns on during winter within city no matter how long i drive it.

All the symptoms pointed out towards a malfunctioning cooling system.

So I removed the thermostat valve, and both temperature sensors and tested those as per service manual.

both sensors were found OK but the thermostat valve found malfunctioning. It was opening OK (at around 80 Degrees but closed to late i.e 70 Degrees). Replaced it and the situation immediately improved within city. But once I took it to highway, the symptom no 4 above was still there except that the time increased from 2 to 5 mins.

I presumed that the ECU still misinterpreting the thermal sensor signal too low i.e car still not warmed up. So to verify, I installed a 1 K Ohms resistor in parallel with the two wires of sensor and the situation immediately improved even at highways. I left the resistor in place and the latest figures are as follows:

CNG: City = 140 Km/tank Highway= 210 Km/tank
Petrol: City = 9 Km/L Highway = 16 Km/L @ 100 kph

I hope this is useful for some of you who are facing same problems like me