Long Term FT

The scan tool displays a positive or negative percentage. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction in the fuel delivery. 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% indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A positive value significantly greater than 0% indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.

The scan tool displays counts. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction of fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A value significantly below 128 indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A value significantly greater than 128 indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.