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Home >> GMC >> 2003 >> Envoy 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures - 4.2L >> Fuel Systems >> Fuel System Pressure Test >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK -- ENGINE CONTROLS under SELF DIAGNOSTIC SYSTEM in SELF DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article. After performing diagnostic system check, go to next step.
    2. NOTE: Inspect fuel system for damage or external leaks before proceeding with this test.
  2. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Does fuel pump operate? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  3. Verify that adequate fuel is in fuel tank before proceeding with this diagnostic. Turn ignition off. Turn off all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Fuel pump relay may need to be commanded on a few times in order to obtain highest possible fuel pressure. Do not start engine. Command fuel pump relay on with a scan tool. Observe fuel pressure gauge with fuel pump commanded on. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to next step. If no, go to step  10.
    4. NOTE: The fuel pressure may vary slightly when fuel pump stops operating. After fuel pump stops operating, fuel pressure should stabilize and remain constant.
  4. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step  7. If no, go to next step.
  5. Relieve fuel pressure to 10 psi (69 kPa). Monitor fuel pressure gauge for 5 minutes. Does fuel pressure decrease by more than 2 psi (14 kPa)? If yes, go to step  21. If no, go to next step.
  6. Operate vehicle within conditions to reproduce original symptoms. Monitor O2 and fuel trim parameters with a scan tool. Do any of scan tool parameters indicate a lean condition? If yes, go to step  15. If no, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  7. Turn ignition off. Remove vent hose from fuel pressure regulator. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Inspect for a fuel leak from fuel pressure regulator atmospheric vent. Is fuel pressure regulator leaking fuel? If yes, go to step  20. If no, go to next step.
  8. Turn ignition off. Relieve fuel pressure. Disconnect fuel feed hose and fuel return hose from fuel rail pipes. Install Fuel Line Shut-Off Adapters (J-37287) between fuel hoses and fuel rail pipes. Open valves on fuel pipe shut-off adapters. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Bleed air from fuel pressure gauge. Command fuel pump relay on and then off with a scan tool. Close fuel feed pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step  17. If no, go to next step.
  9. Turn ignition off. Open fuel feed pipe shut-off valve. Turn ignition on, with engine off. Command fuel pump relay on and then off with a scan tool. Close fuel return pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step  20. If no, go to step  18.
  10. Is fuel pressure more than 54 psi (375 kPa)? If yes, go to step  12. If no, go to next step.
  11. Is fuel pressure more than zero psi? If yes, go to step  14. If no, go to step  15.
  12. Turn ignition off. Relieve fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Attach a length of flexible hose to fuel rail return pipe. Place open end of flexible fuel hose into an approved gasoline container. Turn ignition on, with engine off. Monitor fuel pressure gauge while fuel pump is operating. Is fuel pressure within 48-54 psi (334-375 kPa)? If yes, go to step  19. If no, go to next step.
  13. Inspect fuel rail outlet passage and fuel rail return pipe for a restriction. Did you find and correct condition? If yes, go to step  22. If no, go to step  20.
  14. Turn ignition off. Relieve fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Install Fuel Line Shut-Off Adapter (J-37287) between fuel return pipe and fuel rail. Open valve in fuel pipe shut-off adapter. Turn ignition on, with engine off. Bleed air from fuel pressure gauge. Monitor fuel pressure gauge. DO NOT allow fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage fuel system. Command fuel pump relay on with a scan tool. Slowly close valve in fuel return pipe shut-off adapter, while fuel pump is operating. Does fuel pressure increase to more than 54 psi (375 kPa)? If yes, go to step  20. If no, go to next step.
  15. Inspect for restricted fuel filter or fuel feed pipe. Did you find and correct condition? If yes, go to step  22. If no, go to next step.
  16. Inspect harness connectors and ground circuits of fuel pump for poor connections. Did you find and correct condition? If yes, go to step  22. If no, go to next step.
  17. Remove fuel sender assembly. Inspect fuel pump flex hose for damage, in-tank fuel pump harness connectors for poor connections, fuel strainer for a restriction and fuel tank for contaminants. Did you find and correct condition? If yes, go to step  22. If no, go to step  21.
  18. Turn ignition off. Raise fuel rail with fuel pipes connected. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Locate and replace leaking fuel injector. After repairs, go to step  22.
  19. Repair restricted fuel return pipe. After repairs, go to step  22.
  20. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step  22.
  21. Replace fuel sender. After replacing fuel sender, go to next step.
  22. Operate system in order to verify repair. Did you correct condition? If yes, system is okay. If no, go to step  3.
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