Specifications

What does Short-Term and Long-Term Fuel Trim mean (STFT / LTFT)?
Short Term Fuel Trend (STFT) - Instantaneous fuel trend indicator - a numeric indicator (-) is rich (+) is
lean. Any deviation from 0% indicates the short term fuel trim is changing the injector pulse width. The
amount of pulse width change depends on how far the short term fuel trim value is from 0%.
Long Term Fuel Trend (LTFT) - The long term fuel trim is a matrix of cells arranged by RPM and MAP.
Each cell of the long term fuel trim is a register like the short term fuel trim. As the engine operating
conditions change, the PCM will switch from cell to cell to determine what long term fuel trim factor to use
in the base injector pulse width equation. A value of 0% indicates that fuel delivery requires no
compensation in order to maintain the PCM commanded air/fuel ratio.
A negative value significantly below 0 percent indicates that the fuel system is rich and the PCM is
reducing the fuel delivery (decreased injector pulse width – trying to reduce the amount of fuel). A positive
value significantly above 0 percent indicates that a lean condition exists and the PCM compensates by
adding fuel (increased injector pulse width – attempting to increase the amount of fuel).