What does high Ltft mean?

Why are the fuel trim numbers high? If LTFT or total fuel trim is greater than plus 10%, the PCM thinks the air/fuel ratio is too lean and it’s adding fuel to bring STFT control to the correct range. This presents three possibilities: Unmeasured air is reaching the combustion chambers.

What causes rich long term fuel trims?

Rich. Running rich means that there is too much gas in the air-fuel mixture. This can happen for a variety of reasons, but in a normally functioning system, the ECU will tell it to cut back on the fuel flow to compensate.

What should my Ltft be at idle?

Good LTFT values should be as close to zero as possible, though they can range from 5 to 8 percent depending on the condition of the engine. If the LTFT is getting up around 10 percent or higher, it usually indicates a problem that needs to be diagnosed.

What does positive long term fuel trim mean?

Both LTFT and STFT can be positive (more fuel) or negative (less fuel) percentages. LTFT and STFT are added together to produce the total fuel trim, and neither should exceed ± 10% in normal operating conditions. Fuel trims (LTFT, STFT, or LTFT+STFT) exceeding ±10% may indicate a problem in the engine or the sensors.

What causes high negative fuel trim?

The MAF sensor overestimates airflow at idle, which causes the negative fuel trim values. It then underestimates airflow at cruising speeds, which accounts for the positive fuel trim values.

How do I reset my long term fuel trim?

This is done by disconnecting the battery, waiting for 10 minutes or so, and/or turning the ignition key to the starter position to discharge the system.

What causes high negative fuel trim at idle?

The MAF sensor overestimates airflow at idle, which causes the negative fuel trim values.

When should I reset fuel trims?

Any time you’re tuning VE or MAF, you should force open loop and disable the open loop STFT. After that, flash the file, start the engine and reset the trims.

How do you reset fuel trims without a scanner?