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Home >> Buick >> 2003 >> Century Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures - 3.1L >> Fuel Systems >> Fuel System Diagnosis >> Diagnostic Procedure
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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 in SELF-DIAGNOSTICS - 3.1L CENTURY, GRAND PRIX & MALIBU article.
    2. CAUTION: Inspect the fuel system for damage, or external leaks, before proceeding with this diagnostic procedure.
  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 .
    3. NOTE: Verify adequate fuel in the fuel tank before proceeding with this diagnostic procedure.
  3. Turn ignition switch to OFF position. Turn OFF all accessories Install Fuel Pressure Gauge (J 34730-1A), or equivalent and the fuel pressure gauge fitting. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON using a scan tool. The fuel pump runs for approximately 2 seconds. Command the fuel pump relay ON using a scan tool to obtain the highest possible fuel pressure. Do not start the engine. Observe the fuel pressure gauge, with the fuel pump relay commanded ON. Is the fuel pressure 52-59 psi (358-405 kPa)? 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 running. After the fuel pump stops running, 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 step  6.
  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 customers concern. Monitor the fuel trim and HO2S parameters using a scan tool. Do any of the scan tool parameters indicate a lean condition? If yes, go to step  17. If no, go to DIAGNOSTIC AIDS .
  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 Vacuum Pump (J 23738-A), or equivalent. 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. Inspect 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 RELIEF . Disconnect the fuel feed hose and the fuel return hose from the fuel rail pipes. Install Fuel Pipe Line Shut-Off Adapters (J 37287), or equivalent, between the fuel hoses and the fuel rail pipes. Open the valves on the shut-off adapters. Turn ignition switch to RUN position, engine OFF. Command the fuel pump relay ON using a scan tool. Bleed the air from the fuel pressure gauge. Close the fuel feed pipe shut-off valve. Command the fuel pump relay ON using a scan tool to obtain the highest possible fuel pressure. 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 relay 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 above 59 psi (407 kPa)? If yes, go to step  14. If no, go to next step.
  13. Is the fuel pressure above 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 RELIEF . Disconnect the fuel return hose from the fuel rail return 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 52-59 psi (358-407 kPa)? If yes, go to step  22. If no, go to next step.
  15. Inspect the fuel rail return pipe and 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 RELIEF . Disconnect the fuel return hose from the fuel rail return pipe. Install the shut-off adapters between the fuel return pipe and the fuel rail. Open the valve in the shut-off adapters. 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 relay ON using a scan tool. Does the fuel pressure rise above 52 psi (358 kPa)? If yes, go to step  23. If no, go to next step.
  17. Inspect the fuel filter and 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. Inspect the harness connectors and ground circuits of the fuel pump 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. Inspect the fuel pump flex hose for damage, the in-tank fuel pump harness connectors for poor connections, the fuel strainer for a restriction and 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 relay 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 line. After repair, go to step  25.
  23. Inspect for a missing or damaged fuel pressure regulator "O" ring before replacing the fuel pressure regulator. Replace the fuel pressure regulator if "O" ring is okay. 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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