What causes negative STFT?
Negative fuel trim percentages indicate the PCM is attempting to lean out the fuel mixture, to compensate for a perceived rich condition. STFT and LTFT percentages are the adjustments made by the PCM to maintain the 14.7:1 ratio.
What does a negative Ltft mean?
If the LTFT is negative, it means the ECU has been reducing fuel to maintain an ideal fuel mix. Which basically means the car is running rich. If LTFT is positive, it means the ECU is adding fuel which is an indication that the car is running lean. Normally LTFT should be between -10 to +10 percent.
What should my Stft be at idle?
Ideally, the STFT and LTFT should be within a few percentage points of zero when the engine is idling or being held at a steady RPM. 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.
What should my STFT be at idle?
What should STFT be at idle?
Why is the LTFT so negative at idle?
At idle the LTFT stays very negative between -25 to -33. The STFT stays close to zero. I don’t really understand why the LTFT is very negative, because the O2 sensor reading is normal and based on that the LTFT should stay close to zero.
What does a negative long term fuel trim mean?
LTFT (long term fuel trim) should not change instantly, it is a learned response that happens over time. If the STFT stays consistently negative or positive for a long period of time. That will show up in the LTFT. If the LTFT is negative, it means the ECU has been reducing fuel to maintain an ideal fuel mix.
Why do I get negative LTFT on my M5?
Negative LTFT’s with the engine warm, low RPM. In other words, if left uncorrected, the engine would be running too rich. Common reasons for this include over-reading MAF’s, excessive fuel rail pressure and leaky fuel injectors. I don’t see how a fresh-from-Bavaria M5 would suffer from any of these.
What causes a negative LTFT on a car?
Negative LTFT’s with the engine warm, low RPM. In other words, if left uncorrected, the engine would be running too rich. Common reasons for this include over-reading MAF’s, excessive fuel rail pressure and leaky fuel injectors.