PFI System Check
PFI SYSTEM CHECK is an organized approach for identifying a problem caused by PFI system. Driver comments normally fall into one of the following: steady SERVICE ENGINE SOON light, driveability problems, engine will not start, or engine stalls after start.
Test Number 1) ECM grounds SERVICE ENGINE SOON light during cranking. If light comes on when cranking, ECM is getting power and ground.
Test Number 2) If SERVICE ENGINE SOON light is on when engine is running, check for ECM codes. Diagnose codes before proceeding with PFI SYSTEM CHECK.
Test Number 3) After codes are corrected, ability of PFI system to control fuel delivery to engine must be checked.
Test Number 4) Checks for proper closed/open loop operation.
Test Number 5) If closed loop is achieved, fuel system has to be checked for rich, lean or proper fuel control. PFI system has ECM data ED36 and ED37 integrator, which monitors oxygen sensor rich or lean status and drives fuel system richer if oxygen sensor is lean, or leaner if sensor is rich.
Integrator has a range of 51-204 counts. Integrator value will be 128 when ECM does not have to modify fuel rate to engine. Integrator will reset to 128 if fuel system is in acceleration, power enrichment, some deceleration or open loop modes. Integrator resets to 128 when oxygen sensor is not in control of fuel.
If integrator sees an oxygen sensor that is lean most of the time, integrator value will go higher to try and add more fuel to engine. If integrator sees an oxygen sensor that is rich most of the time, integrator value will go lower to try and drive fuel system leaner.