Fuel System

With this condition, the engine may actually run rich of stoichiometry (14.7:1 air/fuel ratio) if the PCM is not able to compensate enough to correct for the condition. This situation can be caused by a fuel delivery system that is delivering excessive fuel to the engine.

Examples:

• Fuel injector leaks (injector delivers extra fuel).
• EVAP canister purge valve leak (if canister is full of vapors, introduces extra fuel).
• Fuel rail pressure sensor (electronic returnless fuel systems) concern causes sensor to indicate lower pressure than actual. PCM commands higher pressure to the fuel pump driver module (FPDM), causing high fuel pressure (system rich at all airflows).