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Diagnostic Procedure

NOTE: Verify that adequate fuel is in the fuel tank. Check the fuel system for damage, or external leaks, before proceeding with this diagnostic procedure.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article.
  2. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Does the fuel pump operate? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS (EXCEPT PARK AVENUE)  or FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS (PARK AVENUE)  .
  3. Turn ignition switch to OFF position. Turn OFF all accessories. Install Fuel Pressure Gauge (J 34730-1A), or equivalent, to the fuel pressure connection, located on the fuel rail. See Figure. Turn ignition switch to RUN position, engine OFF. The fuel pump may need to be commanded ON a few times, to obtain the highest possible fuel pressure. Do NOT start the engine. Command the fuel pump ON using a scan tool. Observe the fuel pressure gauge, with the fuel pump commanded ON. Is the fuel pressure 53-59 psi (364-405 kPa) on models without supercharger (VIN K) or 48-54 psi (334-375 kPa) on models with supercharger (VIN 1)? If yes, go to next step. If no, go to step  12.
    4. NOTE: The fuel pressure may vary slightly when the fuel pump stops operating. After the fuel pump stops operating, the fuel pressure should stabilize and remain constant.
  4. Monitor the fuel pressure gauge for one minute. Does the fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step  9. If no, go to next step.
  5. Relieve the fuel pressure to 10 psi (69 kPa). Monitor the fuel pressure gauge for 5 minutes. Does the fuel pressure decrease by more than 2 psi (14 kPa)? If yes, go to step  24. If no, go to next step.
  6. Turn ignition switch to OFF position for 15 seconds. Turn ignition switch to RUN position, engine OFF. Monitor the fuel pressure gauge. Start the engine. Does the fuel pressure decrease by 3-10 psi (21-69 kPa) when the engine is started? If yes, go to next step. If no, go to step  8.
  7. Operate the vehicle within the conditions of the customer's concern. Monitor the fuel related parameters using a scan tool. Do any of the scan tool parameters indicate a lean condition? If yes, go to step  17. If no, diagnose by symptom. See SYMPTOMS in TROUBLE SHOOTING - NO CODES - 3.8L BONNEVILLE, GRAND PRIX, IMPALA, LESABRE, MONTE CARLO, PARK AVENUE & REGAL article.
  8. Disconnect the vacuum hose from the fuel pressure regulator. Monitor the fuel pressure gauge. Idle the engine. Apply 12-14 in Hg. (34-47 kPa) of vacuum to the fuel pressure regulator using a hand held vacuum pump. Does the fuel pressure decrease by 3-10 psi (21-69 kPa) when the vacuum is applied? If yes, go to step  21. If no, go to step  23.
  9. Turn ignition switch to OFF position. Remove the vacuum hose from the fuel pressure regulator. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Check for a fuel leak from the fuel pressure regulator vacuum port. Is the fuel pressure regulator leaking fuel? If yes, go to step  23. If no, go to next step.
  10. Turn ignition switch to OFF position. Relieve the fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect the fuel feed hose and the fuel return hose from the fuel rail pipes. Install Fuel Line Shut-off Adapters (J 37287), or equivalent, between the fuel hoses and the fuel rail pipes. Open the valves on the fuel pipe shut-off adapters. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Bleed the air from the fuel pressure gauge. Command the fuel pump ON and then OFF using a scan tool. Close the fuel feed pipe shut-off valve. Monitor the fuel pressure gauge for one minute. Does the fuel pressure remain constant? If yes, go to step  19. If no, go to next step.
  11. Turn ignition switch to OFF position. Open the fuel feed pipe shut-off valve. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON and then OFF using a scan tool. Close the fuel return pipe shut-off valve. Monitor the fuel pressure gauge for one minute. Does the fuel pressure remain constant? If yes, go to step  23. If no, go to step  20.
  12. Is the fuel pressure more than 59 psi (405 kPa) on models without supercharger (VIN K) or 54 psi (375 kPa) on models with supercharger (VIN 1)? If yes, go to step  14. If no, go to next step.
  13. Is the fuel pressure more than zero psi (zero kPa)? If yes, go to step  16. If no, go to step  17.
  14. Turn ignition switch to OFF position. Relieve the fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect the fuel return hose from the fuel rail pipe. Attach a length of flexible fuel hose to the fuel rail outlet passage. Place the open end of the flexible fuel hose into an approved gasoline container. Turn ignition switch to RUN position, engine OFF. Monitor the fuel pressure gauge while the fuel pump is operating. Is the fuel pressure 53-59 psi (364-405 kPa) on models without supercharger (VIN K) or 48-54 psi (334-375 kPa) on models with supercharger (VIN 1)? If yes, go to step  22. If no, go to next step.
  15. Check the fuel rail return pipe and the fuel rail outlet passage for a restriction. Did you find and correct the condition? If yes, go to step  25. If no, go to step  23.
  16. Turn ignition switch to OFF position. Relieve the fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect the fuel return hose from the fuel rail pipe. Install the Fuel Line Shut-off Adapters between the fuel return pipe and the fuel rail. Open the valve in the fuel pipe shut-off adapter. Turn ignition switch to RUN position, engine OFF. Bleed the air from the fuel system. Monitor the fuel pressure gauge. Do NOT allow the fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage the fuel system. Slowly close the valve in the fuel return pipe shut-off adapter. Command the fuel pump ON using a scan tool. Does the fuel pressure increase to more than 59 psi (405 kPa) on models without supercharger (VIN K) or 54 psi (375 kPa) on models with supercharger (VIN 1)? If yes, go to step  23. If no, go to next step.
  17. Check the fuel filter and the fuel feed pipe for a restriction. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  18. Check the fuel pump harness connectors and the ground circuits for poor connections. Did you find and correct the condition? If yes, go to step  25. If no, go to next step.
  19. Remove the fuel sender assembly. Check the fuel pump flex hose for damage, the in tank fuel pump harness connectors for poor connections, the fuel strainer for a restriction and for contaminates in the fuel tank. Did you find and correct the condition? If yes, go to step  25. If no, go to step  24.
  20. Turn ignition switch to OFF position. Raise the fuel rail, with the fuel lines connected. Turn ignition switch to RUN position, engine OFF. Command the fuel pump ON using a scan tool. Locate and replace the leaking fuel injector. After repair, go to step  25.
  21. Repair the vacuum source to the fuel pressure regulator. After repair, go to step  25.
  22. Locate and repair the restricted fuel return pipe. After repair, go to step  25.
  23. Check for a missing or damaged fuel pressure regulator "O" ring seal before replacing the fuel pressure regulator. Replace the fuel pressure regulator. After repair, go to step  25.
  24. Replace the fuel pump. After repair, go to next step.
  25. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step  3.
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