Why is my long-term fuel trim high?

Why is my long-term fuel trim high?

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.

How do you diagnose fuel trims?

To test a rich response, you can feed some propane vapor from a small propane tank into the throttle body or a vacuum hose connection on the intake manifold. This time, you should see a drop in fuel trim readings, with STFT going NEGATIVE, and LTFT creeping downward in response to the rich fuel mixture.

What causes positive fuel trims?

Here are some common causes of positive long-term fuel trim: Air or vacuum leaks in the intake manifold, throttle body or in a vacuum hose. Defective fuel pump not generating enough pressure or volume. Restricted fuel flow due to pinched hose or plugged filter.

How do I reset my long-term fuel trim?

To perform a PCM reset…

1. Bring car up to normal operating temp.
2. Turn ignition off.
3. Remove ECM main fuse.
4. Turn ignition to “on”, do not start.
5. Wait for system check to complete, numerous errors will be detected.
6. Turn ignition off.
7. Replace fuse.
8. Turn ignition to “on” and wait for system check.

What should my long term fuel trim be?

Long-term fuel trim values Ideally, long-term fuel trims should be at, or close to 0% when the engine is running at a steady speed. However, while changes to the engine speed will (and must) produce changes in the long-term fuel trim value, this value should return to a point close to 0% when the engine speed steadies.

What is the difference between long term and short term fuel trim?

Long-term fuel trim relies on sensors further downstream in the exhaust system, past the catalytic converter. While the sensors’ signal will fluctuate frequently upstream, where short-term fuel trim is measured, the signal at the sensors further down should be fairly constant.

What could cause a rich air/fuel mixture?

Therefore, a corrupt signal indicating a colder than an actual engine will result in a rich air-fuel mixture. A faulty oxygen sensor sending the wrong signal to the engine control module can result in a rich fuel condition. Symptoms include black-colored exhaust, fouled spark plugs, and poor engine performance.

When to take a long term fuel trim?

Note also that fuel trim values should only be taken when the engine had been running at the above speeds for at least 30 seconds. Ideally, long-term fuel trims should be at, or close to 0% when the engine is running at a steady speed.

What kind of fuel trim is running rich?

Okay, next issue… my car is running a little bit rich. Scanning it and reading about -8% LT when idling. When at around 25% throttle and 50kpa MAP LT fuel trim is just -1%. Pressing the throttle a little bit more and at higher MAP I get -4% to -8%. Values are not that much off so the check engine lights is not on and no DTC thrown.

What causes incorrect fuel trim on lean running engine?

O2 or A/F sensor faults (improper feedback due to a “shifted” or biased sensor); shorted or open O2 sensor or wiring; faulty O2 sensor heater circuit operation. Finally, other wiring, sensor or PCM faults may also cause incorrect base-fuel or fuel-trim calculations.

Is the DTC in the LT Fuel trim?

Values are not that much off so the check engine lights is not on and no DTC thrown. I have been driving for a while so the LT Fuel trim is stable. When I first bought the car it had DTC P0172, but after a reset it didn’t come back.