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Diagnostic Procedure

NOTE: Fuel Pipe Shut-Off Adapters (J 37287) are required for this procedure.
  1. If diagnostic system check has already been performed, go to next step. If diagnostic system check has not been performed, go to go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.6L DEVILLE & SEVILLE article.
    2. NOTE: Inspect fuel system for damage or external leaks before proceeding with this diagnostic.
  2. Turn ignition ON, with engine OFF. Using scan tool, command fuel pump ON. Does fuel pump operate? If yes, go to next step. If no, go to FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS .
    3. NOTE: Ensure there is adequate fuel in fuel tank before proceeding with this diagnostic
    NOTE: Disconnecting negative battery cable is not necessary for this procedure.
  3. Turn ignition OFF. Turn OFF all accessories. Install Fuel Pressure Gauge (J-34730-1A). See FUEL SYSTEM PRESSURE RELEASE . Place bleed hose from fuel pressure gauge into an approved gasoline container. Turn ignition ON, with engine OFF. Using scan tool, command fuel pump ON. Bleed air out of fuel pressure gauge. It may be necessary to command the fuel pump ON several times in order to obtain the highest possible fuel pressure. DO NOT start engine. Observe fuel pressure gauge, with fuel pump commanded ON. Is fuel pressure within 41-47 psi (284-325 kPa). If yes, go to next step. If no, go to step  12.
    4. NOTE: Fuel pressure may vary slightly when fuel pump stops running. After fuel pump stops running, fuel pressure should stabilize and remain constant.
  4. Monitor fuel pressure gauge for one minute. Does fuel pressure drop more than 5 psi (34 kPa)? If yes, go to step  9. If no, go to next step.
  5. Relieve fuel pressure to 10 psi (69 kPa). Monitor fuel pressure gauge for 5 minutes. Does fuel drop more than 2 psi (14 kPa). If yes, go to step  25. If no, go to next step.
  6. Turn ignition OFF for 15 seconds. Turn ignition ON, with engine OFF. Monitor fuel pressure gauge. Start engine. Does fuel pressure drop 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 the conditions of the customer's concern. Monitor fuel related parameters with 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 TROUBLE SHOOTING - NO CODES - 4.6L DEVILLE & SEVILLE article.
  8. Disconnect vacuum hose from fuel pressure regulator. Operate engine at idle. Monitor fuel pressure gauge. Using a hand-held vacuum pump, apply 12-14 in. (304-355 mm ) to fuel pressure regulator. Does the fuel pressure drop 3-10 psi (21-69 kPa) when vacuum is applied? If yes, go to step  22. If no, go to step  24.
  9. Turn ignition OFF. Disconnect vacuum hose from fuel pressure regulator. Turn ignition ON, with engine OFF. Using scan tool, command fuel pump ON. Inspect for fuel leak from fuel pressure regulator vacuum port. Is fuel pressure regulator leaking fuel? If yes, go to step  24. If no, go to next step.
  10. Turn ignition OFF. Relieve fuel pressure. Disconnect fuel feed hose and fuel return hose from fuel rail pipes. See FUEL LINE DISCONNECT FITTINGS under FUEL SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Install Fuel Pipe Shut-Off Adapters between the fuel hoses and fuel rail pipes. Open valves on the Fuel Pipe Shut-Off Adapters. Turn ignition ON, with engine OFF. Using scan tool, command fuel pump ON. Bleed air from fuel pressure gauge. Command the fuel pump ON and then OFF. Close fuel feed pipe shut-off valve. Monitor 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 OFF. Open fuel feed pipe shut-off valve. Turn ignition ON, with engine OFF. Command fuel pump ON and then OFF with a scan tool. Close the fuel return pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step  24. If no, go to step  20.
  12. Is fuel pressure greater than 62 psi (427 kPa)? If yes, go to step  14. If no, go to next step.
  13. Is fuel pressure greater than zero psi (0 kPa)? If yes, go to step  16. If no, go to step  17.
  14. Turn ignition OFF. Relieve fuel pressure. Disconnect fuel return hose from fuel rail pipe. Attach a length of flexible fuel hose to fuel rail outlet passage. Place open end of 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 41-47 psi (284-325 kPa)? If yes, go to step  23. If no, go to next step.
  15. Inspect fuel return pipe and fuel rail outlet passage for restriction. Repair as necessary. After repairs, go to step  26. If no restriction found, go to step  24.
    16. NOTE: DO NOT allow the fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage the fuel system.
  16. Turn ignition OFF. Relieve fuel pressure. Disconnect fuel return hose from fuel rail pipe. Install Fuel Pipe Shut-Off Adapters between fuel return pipe and fuel rail. Open valve in fuel pipe shut-off adapter. Turn ignition ON, with engine OFF. Command fuel pump ON with scan tool. Bleed air from fuel system. Monitor fuel pressure gauge. Slowly close the valve in fuel return pipe shut-off adapter. Command fuel pump ON with scan tool. Does the fuel pressure rise to more than 47 psi 325 kPa)? If yes, go to step  24. If no, go to next step.
  17. Check for restriction in fuel filter and fuel feed pipe. Repair as necessary. After repairs, go to step  26. If no restriction found, go to next step.
  18. Inspect harness connectors and ground circuits of fuel pump for poor connections. Repair as necessary. After repairs, go to step  26. If harness connectors and ground circuits okay, 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 or contaminates in fuel tank. Repair as necessary. After repairs, go to step  26. If no problem found, go to step  25.
  20. Turn ignition OFF. Raise fuel rail with fuel lines connected. See FUEL RAIL & INJECTORS under FUEL SYSTEMS in REMOVAL & INSTALLATION - DEVILLE & SEVILLE article. Turn ignition ON, with engine OFF. Using scan tool, command fuel pump ON. Locate and replace leaking fuel injector(s). After repairs, go to step  26.
    21. NOTE: Ensure that the fuel injectors are fully seated in the fuel rail before proceeding with this step.
  21. Position the fuel rail assembly over the intake manifold ports. Reinstall the fuel rail retaining bolts by hand. Turn ignition ON, with the engine OFF. Observe the fuel pressure gauge. Allow the fuel pressure to drop to 15 psi (103 kPa). Raise the fuel rail in order to locate and replace the leaking fuel injector. After repairs, go to step  26.
  22. Repair vacuum source to fuel pressure regulator. After repairs, go to step  26.
  23. Locate and repair the restricted fuel return line. After repairs, go to step  26.
    24. NOTE: Inspect for a missing, or damaged, fuel pressure regulator O-ring seal before replacing the fuel pressure regulator.
  24. Replace fuel pressure regulator. After repairs, go to step  26.
  25. Replace fuel pump. After repairs, go to next step.
  26. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step  3.
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