Long Term FT-1

The scan tool display is 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 desired air/fuel ratio. A negative value, significantly below 0%, indicates that the fuel system is rich. When the fuel system is rich, the PCM reduces fuel delivery by decreasing injector pulse width. A positive value, significantly greater than 0%, indicates that a lean condition exists. During a lean condition the PCM increases fuel delivery by increasing injector pulse width. Fuel trim values at maximum authority may indicate an excessively rich or lean condition.