How much is too much fuel trim long term?

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 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’s the difference between long term and short term fuel trim?

Fuel trim is reported in two different forms: long-term fuel trim (LTFT) and short-term fuel trim (STFT). Fuel trim is related to a variety of sensors and variables. Why do we need Fuel Trim? The engine controller (ECM or PCM) constantly compensates for changing conditions by adjusting the amount of fuel injected into each port or cylinder.

When do fuel trims go up or down?

Usually, they’ll stay within %5 +/- of zero. On an older engine, they may go up towards 10% at times. The long-term fuel trims (LTFT) are driven by the short-term fuel trims. LTFT refers to changes in STFT but averaged over a longer period of time.

When to use LTFT or STFT fuel trim?

What should the normal fuel trim reading be?

A normal long-term fuel trim reading will appear to stay the same, giving a long-term average of fuel added. It, too, should be close to zero, positive, or negative single digits under normal circumstances.

What’s the fuel trim on a Chevy truck?

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.

Is there a fuel trim issue on my Vortec?

Its not making sense that my short term trims are bouncing around from 0 to +7 while my long term trims are +20 to +25. Maybe a reset is in order? I will fully understand these trims someday haha. Re: Fuel Trim issue? GMT604 wrote: If you clear the memory, idling for about ten minutes should tell you.

How much is too much fuel trim long term?