PFI System Check

After the VISUAL INSPECTION  is complete, the PFI system check should be performed. The PFI system check will provide direction for diagnosis of:

• PCM inoperative or damaged due to water intrusion or electrical overload (No PCM data or "Service Engine Soon" telltale inoperative).
• PCM trouble codes current or history.
• Fuel System Rich or Lean.
• Customer Complaint Driveability Symptoms.

The PFI System Check is designed as a "Master" chart for driveability and emissions system diagnosis. The System Check should always be used as the starting point for all PFI diagnosis. The PFI System Check is an organized approach for identifying a problem caused by the Port Fuel Injection System. Driver comments normally fall into one of the following areas:

• Steady "Service Engine Soon" telltale.
• Driveability problem.
• Engine will not start or stall after start.

Understanding the PFI System Check flow chart, see , and using it correctly will reduce diagnosis time and prevent the unnecessary replacement of parts.

1. The PCM grounds the "Service Engine Soon" telltale when cranking. If the telltale comes on when cranking, then the PCM is getting power and ground.
2. If the "Service Engine Soon" light is on with engine running, check for PCM codes. Diagnose the codes before proceeding with the "System Check". For information on the proper procedure to diagnose PCM and BCM codes, see SELF-DIAGNOSTICS  . For BCM code diagnosis, see BODY COMPUTER MODULE article.
3. After codes are corrected, the ability of the PFI system to control the fuel delivery to the engine must be checked.
4. Checking for proper closed/open loop operation.
5. If closed loop is achieved, the fuel system has to be checked for rich, lean or proper fuel control. The system has PCM Data ED36 and ED37 "Integrator" which monitors the oxygen sensor rich/lean status and drives the fuel system richer if the oxygen sensor is lean and leaner if the sensor is rich. The integrator has a range of 51 counts to 204 counts. The integrator value will be 128 when the PCM does not have to modify the fuel rate to the engine. The integrator will reset to 128 if the 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 the integrator sees an oxygen sensor that is lean most of the time, the integrator value will go higher to try and add more fuel to the engine. If the integrator sees an oxygen sensor that is rich most of the time, the integrator value will go lower to try and drive the fuel system leaner. In this test, operate the engine at closed loop, 1000-2000 RPM with steady throttle to stabilize the integrator reading of 88-160. In most cases, this will indicate that the fuel delivery system is OK.