Long Term Fuel Trim

Long Term Fuel Trim Description
The Long Term FT consist of groups of fuel control calibrations or cells. Each cell contains the short and long term fuel injector control values required to maintain the correct air and fuel mixture for a particular long term engine operating condition. The control module monitors the short term fuel trim values in order to determine if the short term fuel trim values are indicating a trend of rich or lean corrections to the fuel control. If the control module determines that the short term fuel trim is able to maintain control and is near 0 percent (128 counts), the

Long Term FT within that particular cell will indicate a value of 0 percent (128). If the control module determines that the fuel system is operating rich, Long Term FT will compensate for the rich condition by decreasing the injector pulse width, and a Long Term FT value of less than 0 percent (128 counts) is indicated. If the control module determines that the fuel system is operating lean, Long Term FT will compensate for the lean condition by increasing the injector pulse width and a Long Term FT value of more than 0 percent (128 counts) is indicated. If the control module determines that the Long Term FT values indicate a trend toward a rich or a lean correction within that cell, the control module will switch to the appropriate cell, either rich or lean, and the short term value will return to 0 percent (128).