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Home >> Chevrolet >> 2003 >> Avalanche 2500, RWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures - 8.1L >> 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 - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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 - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL 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 55-62 psi (379-427 kPa)? If yes, go to next step. If no, go to step  12 .
    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  8 . If no, go to next step.
  5. Release 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  22 . If no, go to next step.
  6. Turn ignition on, with engine off. Monitor fuel pressure gauge. Start engine. Does fuel pressure decrease by 3-10 psi (21-69 kPa) when engine is started? If yes, go to next step. If no, go to step  8 .
  7. 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  17 . If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
  8. Disconnect vacuum hose from fuel pressure regulator. Monitor fuel pressure gauge. Idle engine. Apply 12-14 inches of vacuum to fuel pressure regulator with a hand-held vacuum pump. Does fuel pressure drop 3-10 psi (21-69 kPa) when vacuum is applied? If yes, go to step  21 . If no, go to step  23 .
  9. Turn ignition off. Disconnect vacuum hose from fuel pressure regulator. Turn ignition on, with engine off. Command fuel pump ON with a scan tool. Inspect for a fuel leak from vacuum port of fuel pressure regulator . Is fuel pressure regulator leaking fuel? If yes, go to step  23 . If no, go to next step.
  10. Turn ignition off. Release fuel pressure. Disconnect fuel feed hose and fuel return hose from fuel rail. 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 ON with a scan tool. Bleed air from fuel pressure gauge. Command fuel pump ON and 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  19 . If no, go to next step.
  11. Turn ignition off. Open shut-off valve for fuel feed pipe. Turn ignition on, with engine off. Command fuel pump ON and OFF with a scan tool. Close shut-off valve for fuel return pipe. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step  23 . If no, go to step  20 .
  12. Is fuel pressure more than 62 psi (427 kPa)? If yes, go to step  14 . If no, go to next step.
  13. Is fuel pressure more than zero psi? If yes, go to step  16 . If no, go to step  17 .
  14. Turn ignition off. Release 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 55-62 psi (379-427 kPa)? If yes, go to step  22 . If no, go to next step.
  15. Inspect fuel rail outlet passage and fuel rail return pipe for a restriction. Did you find and correct condition? If yes, go to step  25 . If no, go to step  23 .
  16. Turn ignition off. Release 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 62 psi (427 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 62 psi (427 kPa)? If yes, go to step  23 . If no, go to next step.
  17. Inspect for restricted fuel filter or fuel feed pipe. Did you find and correct condition? If yes, go to step  25 . If no, go to next step.
  18. Inspect harness connectors and ground circuits of fuel pump for poor connections. Did you find and correct condition? If yes, go to step  25 . If no, go to next step.
  19. 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  25 . If no, go to step  24 .
  20. Turn ignition off. Raise fuel rail with fuel lines connected. Turn ignition on, with engine off. Command fuel pump relay ON with scan tool. Locate and replace leaking fuel injector. After repairs, go to step  25 .
  21. Repair vacuum source to fuel pressure regulator. After repairs, go to step  25 .
  22. Repair restricted fuel return pipe. After repairs, go to step  25 .
  23. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step  25 .
  24. Replace fuel pump. After replacing fuel pump, go to next step.
  25. 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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