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Fuel System Diagnosis

WARNING: Begin fuel system diagnosis with fuel system pressure test. Relieve fuel system pressure before disconnecting any components or installing fuel pressure gauge.
  1. Perform On-Board Diagnostic II (OBD-II) System Check. See ON-BOARD DIAGNOSTIC (OBD-II) SYSTEM CHECK in TESTS W/CODES - INTRODUCTION article. After performing OBD-II system check, go to next step.
  2. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEM. Connect Fuel Pressure Gauge (J-34730-1A ) to fuel pressure test port. Turn ignition on with engine off. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm2 ) and should hold steady. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 8).
  3. Turn ignition off for 10 seconds. Ensure A/C is off, if equipped. Turn ignition on. Fuel pump should run for 2 seconds. Observe fuel pressure after pump stops. If pressure is 60-66 psi (4.2-4.6 kg/cm2 ) and holds steady, go to step 5). If pressure is not within specification, or is within specification but does not hold, go to next step.
  4. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELEASE  under FUEL SYSTEM. Remove fuel filter and drain fuel from lines into acceptable container. Install 3/8" Fuel Feed Pipe Shut-Off Valve (J42964 ) in place of fuel filter. Ensure valve installation is free of leaks. Idle engine for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on and allow pressure to build. Close shut-off valve and turn ignition off. Pressure should remain constant at 60-66 psi (4.2-4.6 kg/cm2 ). If fuel pressure is as specified, go to step 12). If fuel pressure is not as specified, go to step 6).
  5. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to step 27). If fuel pressure is not suspected of dropping during described conditions, go to step 26).
  6. Inspect fuel feed line between shut-off valve and fuel rail. If no problem is found, go to next step. If problem is found, go to step 25).
  7. Open fuel shut-off valve. Relieve fuel pressure. Drain fuel from lines into approved gasoline container. Install 5/16" Fuel Return Pipe Shut-Off Valve (J42873-2 ) in place of fuel return pipe union at fuel rail. Ensure valve installation is free of leaks. Idle engine for 30 seconds. Turn ignition off for 10 seconds. Turn ignition on and allow pressure to build. Close shut-off valve and turn ignition off. Pressure should remain constant. If fuel pressure remains constant, go to step 22). If fuel pressure does not remain constant, go to step 29).
  8. Turn ignition off for 10 seconds. Ensure A/C is off, if equipped. Turn ignition on with engine off. Pump should operate for 2 seconds. If fuel pressure does not exist, go to next step. If fuel pressure exists, go to step 13).
  9. Turn ignition off. Install fused jumper wire connected to battery voltage to fuel pump test terminal. See WIRING DIAGRAMS article. If fuel pump operates, go to next step. If fuel pump does not operate, see FUEL SYSTEM  under ENGINE CRANKS BUT WILL NOT START.
  10. Inspect fuel system for restricted fuel lines, plugged fuel filter or clogged fuel pump strainer. If problem was found, go to next step. If no problem was found, go to step 12).
  11. Repair or replace components causing fuel system restriction as necessary. Go to step 30).
  12. Disconnect negative battery cable. Raise vehicle on hoist. Lower fuel tank sufficiently to disconnect fuel hoses and electrical connectors. Remove fuel tank. Remove and replace fuel tank sender unit module. After repair, go to step 30).
  13. Turn ignition off for 10 seconds. Turn ignition on with engine off. Pump should operate for 2 seconds. Monitor fuel pressure. Fuel pressure should be 66 psi (4.6 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 15).
  14. Relieve fuel pressure. Disconnect engine compartment fuel return line. Install flex fuel line to return line. Insert other end of flex fuel line into approved container. Turn ignition on and monitor fuel pressure within 2 seconds. Fuel pressure should be 60-66 psi (4.2-4.6 kg/cm2 ). If fuel pressure is as specified, go to step 16). If fuel pressure is not as specified, go to step 17).
  15. Turn ignition off for 10 seconds. Turn ignition on with engine off. Pump should operate for 2 seconds. Monitor fuel pressure Fuel pressure should be 60 psi (4.2 kg/cm2 ). If fuel pressure is as specified, go to step 19). If fuel pressure is not as specified, go to step 30).
  16. Locate and repair restriction in fuel return line. After repair, go to step 30). If no restriction was found, go to next step.
  17. Visually and physically inspect fuel return line for restriction where is was disconnected. If restriction was found, go to next step. If no restriction was found, go to step 22).
  18. Replace faulty engine fuel lines as necessary. After repair, go to step 30).
  19. Check for restricted fuel line or fuel filter. If problem was found, go to next step. If no problem was found, go to step 21).
  20. Repair or replace faulty fuel filter and/or fuel line(s) as necessary. After repair, go to step 30)
    NOTE: DO NOT  permit fuel pressure to rise to more than 75 psi (5.3 kg/cm2 ).
  21. Relieve fuel pressure. Drain fuel from lines into acceptable container. Install 5/16" Fuel Return Pipe Shut-Off Valve (J42873-2) in place of fuel return pipe union located near fuel filter. Ensure valve installation is free of leaks. Turn ignition off for 10 seconds. Turn ignition on and bleed air from pressure gauge into approved fuel container. Connect 20-amp fused jumper wire between battery voltage and fuel pump test terminal. See WIRING DIAGRAMS article. While monitoring pressure gauge, slowly close shut-off valve on fuel return line. Fuel pressure should be greater than 66 psi (4.6 kg/cm2 ). If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 23).
  22. Replace fuel pressure regulator. After repair, go to step 30).
  23. Check fuel pump for loose or corroded connections, pump motor binding, and poor ground connection. Also check for faulty or incorrect fuel pump. If problem is found, go to next step. If no problem is found, go to step 12).
  24. Repair or replace fuel system components as necessary. After repair, go to step 30).
  25. Replace faulty fuel feed line and go to step 30).
  26. Start engine and let it idle until normal operating temperature is reached. While monitoring fuel pressure, open throttle quickly. Fuel pressure should quickly increase to almost 66 psi (4.6 kg/cm2 ). If fuel pressure is not as specified, go to next step. If fuel pressure is as specified, fuel system is operating correctly.
  27. Inspect fuel system components for leaks or restrictions. Ensure correct fuel pump is installed. If problem is found, go to next step. If no problem is found, go to step 12).
  28. Repair or replace faulty fuel system component(s) as necessary. After repair, go to step 30).
  29. Locate and replace leaking injector(s). After repair, go to next step.
  30. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If additional DTC(s) are stored, diagnose and clear DTC(s). See appropriate TESTS W/CODES - INTRODUCTION article. If DTC(s) are not present, system is okay.
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