Download The ECU modifies the injection rate under two areas of engine operation. These areas are the idle or low load mid range engine operation and operation under a normal to higher load when at higher engine speeds. These altered injection rates are known as Long Term Fuel Trim (LTFT) Additive and Short Term Fuel Trim (STFT) Multiplicative. See figure 1.
Long Term Fuel Trim (LTFT)
This is the control of Injection Pulse Time Open (ti) (also called Injection Pulse Width) over the entire range of engine operation. It is primarily calculated at idle or low load mid range engine operation and is averaged over time.