Low Fuel Efficiency Issues with My 2006 Toyota Belta 1.3

The poor fuel efficiency of your 2006 Toyota Belta 1.3 2SZ-FE with a swapped engine and CVT transmission may stem from several factors, given the extensive diagnostics and maintenance you’ve already performed. Below are possible areas to investigate further:

Oversized Tires:
While you’ve noted the oversized tires 185/65 R15, they can have a significant impact on fuel efficiency. Larger tires increase rolling resistance and alter the effective gear ratio, which can strain the engine and CVT, leading to reduced mileage. Consider reverting to the stock tire size likely 165/70 R14 o r 175/65 R14 to test if this improves efficiency.

CVT Transmission Issues:
The slight jerking at low speeds and perceived gear slip under full throttle may indicate issues with the CVT. Problems like a worn CVT belt, low-quality transmission fluid, o r incorrect fluid levels can significantly impact performance and mileage. Check the CVT fluid level and condition, ensuring it meets Toyota’s specifications e.g., Toyota CVT TC o r FE fluid. If not already done, replace the CVT fluid with the correct type and quantity.

Fuel System Calibration:
While your fuel trim values appear normal, the O2 sensor readings suggest the engine is running rich high O2S1 voltage most of the time. This could result from:
ECU Calibration o r Adaptation: Reset the ECU to clear learned adaptations, especially after replacing components like the O2 sensor o r MAF.
Thermostat o r ECT Sensor: If the engine isn’t reaching optimal operating temperature, it could stay in a fuel-rich mode. Verify the thermostat and Engine Coolant Temperature ECT sensor operation.

Vacuum Leaks:
Minor vacuum leaks might not cause drastic fuel trim deviations but could still impact combustion efficiency. Perform a smoke test to identify any hidden leaks.

Catalytic Converter Efficiency:
Even after cleaning the catalytic converter, it might not be functioning optimally. A damaged o r partially clogged catalytic converter can cause fuel efficiency issues. Verify its performance using OBD-II data o r a professional emissions test.

Swapped Engine Compatibility:
Since this is a swapped engine, ensure that the ECU and all sensors are compatible with the 2SZ-FE engine. Sometimes, mismatched components o r wiring can lead to suboptimal performance. Check if the throttle body, injectors, and intake manifold match the swapped engine specifications.

Driving Patterns and Urban Conditions:
In congested urban settings like Lahore, frequent stops, idling, and short trips can exacerbate fuel consumption. If possible, compare your mileage on a highway drive to gauge the true efficiency of the engine.

Exhaust Gas Recirculation EGR:
A malfunctioning EGR system can affect combustion efficiency. Inspect the EGR valve for blockages o r carbon buildup.

Further Data Analysis:
Your recorded OBD-II data could provide deeper insights. For instance:
O2 Sensor Behavior: O2S2 readings staying high may indicate inefficiency in the catalytic converter o r a rich mixture.
Throttle Position Sensor TPS: Check if the throttle response is smooth and consistent.
Fuel Pressure: Verify that the fuel pressure regulator and pump are operating within specifications.

Suggested Next Steps:

Replace oversized tires with stock sizes and monitor changes in mileage.
Inspect and service the CVT transmission, including fluid replacement if not recently done.
Reset the ECU to clear adaptations and verify fuel system calibration.
Check the thermostat, ECT sensor, and potential vacuum leaks.
Perform a highway mileage test to isolate urban driving factors.
Review your OBD-II data for additional anomalies o r trends.