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Home >> Pontiac >> 2002 >> Aztek AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures >> Basic Fuel System Checks (Gasoline) >> Fuel System Pressure Test (4.2L) >> Diagnostic Procedure
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Diagnostic Procedure

  1. Did you perform a Diagnostic System Check-Engine Controls? If yes, go to next step. If no, perform DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER XL article.
    2. NOTE: Inspect fuel system for damage, or external leaks, before proceeding with this test.
  2. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Does fuel pump operate? If yes, go to next step. If no, go to FUEL PUMP RELAY (ALL EXCEPT 2.2L & 3.0L VUE, 3.4L, 5.0L & 5.7L) under FUEL SYSTEMS (GASOLINE) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.
    3. NOTE: Verify that adequate fuel is in fuel tank before proceeding with this test. Fuel pump may need to be commanded ON a few times in order to obtain highest possible fuel pressure. DO NOT start engine.
  3. Turn OFF the ignition. Turn OFF all accessories. Install fuel pressure gauge. Turn ON the ignition, with the engine OFF. Command fuel pump ON with 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: 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 of customer's concern. Monitor fuel related parameters with scan tool. Do scan tool parameters indicate a lean condition? If yes, go to step  15. If no, go to SYMPTOM DIAGNOSIS under SYMPTOMS (GASOLINE) in TROUBLE SHOOTING - NO CODES - TRUCKS article.
  7. Turn OFF the ignition. Remove vent hose from fuel pressure regulator. Turn ON the ignition, with the engine OFF. Command fuel pump ON with 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 OFF the ignition. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel feed hose and fuel return hose from fuel rail pipes. See FUEL LINE DISCONNECT FITTINGS under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL & TRAILBLAZER. Install (J 37287) Fuel Line Shut-Off Adapters between fuel hoses and fuel rail pipes. Open valves on fuel pipe shut-off adapters. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Bleed air from fuel pressure gauge. Command fuel pump ON and then OFF with 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 next step. If no, go to step  17.
  9. Turn OFF the ignition. Open fuel feed pipe shut-off valve. Turn ON the ignition, with the engine OFF. Command fuel pump ON and then OFF with 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 0 psi (0 kPa)? If yes, go to step  14. If no, go to step  15.
  12. Turn OFF the ignition. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel feed hose and fuel return hose from fuel rail pipes. See FUEL LINE DISCONNECT FITTINGS under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL & TRAILBLAZER. Attach a length of flexible fuel hose to fuel rail return pipe. Place open end of flexible fuel hose into an approved gasoline container. Turn ON the ignition, with the 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 return pipe and fuel rail outlet passage for a restriction. Did you find and correct the condition? If yes, go to step  22. If no, go to step  20.
  14. Turn OFF the ignition. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE . Disconnect fuel feed hose and fuel return hose from fuel rail pipes. See FUEL LINE DISCONNECT FITTINGS under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL & TRAILBLAZER. Install (J 37287) between fuel return pipe and fuel rail. Open valve in fuel pipe shut-off adapter.
    CAUTION: DO NOT allow fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage fuel system.

    Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Bleed air from fuel system. Monitor fuel pressure gauge. Slowly close valve in fuel return pipe shut-off adapter. Command fuel pump ON with scan tool. Does fuel pressure rise above 54 psi (375 kPa)? if yes, go to step  20. If no, go to next step.

  15. Inspect fuel filter and fuel feed pipe for a restriction. Did you find and correct the 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 the 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 for contaminates in fuel tank. Did you find and correct the condition? If yes, go to step  22. If no, go to step  21
  18. Turn OFF the ignition. Raise fuel rail, with fuel pipes connected. Turn ON the ignition, with the engine OFF. Command fuel pump ON with scan tool. Locate and replace leaking fuel injector. After repairs, go to step  22.
  19. Locate and repair restricted fuel return pipe. After repairs, go to step  22.
    20. NOTE: Inspect for a missing or damaged "O" ring seal before replacing fuel pressure regulator.
  20. Replace fuel pressure regulator. After repairs, go to step  22.
  21. Replace fuel pump. After repairs, go to next step.
  22. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to step  3.
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