If the lean or rich condition recurs during the next 3 warm-up cycles the PCM stores a DTC and illuminates the check engine light. When the PCM calculates it will require pulse width modification outside the upper or lower limits of adjustment to achieve a 14.7:1 air/fuel ratio, a pending DTC is stored. The extent to which the base pulse width can be modified is limited. In a similar manner if the oxygen sensor(s) indicate the engine is running lean, the PCM will correct the lean condition by increasing the fuel injection pulse width. I have followed the Ford OBDII drive cycle as described here I have logged 130 or so miles on the setup so not sure what the deal is. When the fuel system monitor isn’t ready, the PCM can’t control the fuel injection, which leads to a cascade of additional issues. 1 So I have to pass emissions and have gotten all my monitors to enable except for the fuel monitor. Hence a problem with the EVAP system which displays the monitor EVAP not ready, can affect this monitor too. If the oxygen sensor(s) indicate the engine is running rich, the PCM will correct the rich condition by reducing the fuel injection pulse width. The fuel system monitor works optimally when the EVAP system monitor is in good condition. ![]() The fuel trim tables have upper and lower limits for modification of the fuel injection base pulse width needed to maintain a 14.7:1 air/fuel ratio during closed-loop operation. The correction is stored in the fuel trim tables. During closed-loop fuel control, the fuel trim strategy learns the corrections needed to correct for a rich or lean fuel system. Fuel trim tables are based on engine RPM and engine load. The fuel control system uses fuel trim tables stored in the PCMs memory to calculate and compensate for the variability that occurs in fuel system components due to normal wear and aging. ![]() The monitor executes continuously under normal engine operating and driving conditions providing there are no DTCs present and the EVAP system is not purging fuel vapors into the engine. The fuel system monitor allows the PCM to evaluate how close the fuel control system can regulate the fuel mixture in attempting to achieve an optimum air/fuel ratio in the combustion chamber throughout varying engine rpm and load ranges. OBD II Readiness Monitors Continuous Monitors Fuel System Monitor
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