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Diagnostic Aids

Perform this test only when directed by QUICK TEST . This test is intended to diagnose the following:

WARNING: Fuel system remains under high pressure even when engine is not running. To avoid injury, release fuel pressure before disconnecting any fuel system hose or component.
Fig 1: Identifying Fuel Delivery Wiring Circuits
G96H19411Courtesy of FORD MOTOR CO.
Fig 2: Identifying Diagnostic Connector Terminals
G96J01184Courtesy of FORD MOTOR CO.
SYMPTOM DIRECTORY

Symptom Test Step
No Fuel Pressure Go To Step 3)
Low Fuel Pressure Go To Step 20)
High Fuel Pressure Go To Step 30)
Fuel Injector Test Go To Step 40)
  1. 1) Check System Integrity  Turn ignition off. Inspect fuel system for leaks, damaged, kinked or cracked hoses. Inspect wiring harness for damage or loose connectors. Ensure battery is fully charged and fuses are okay. If vehicle does not start, ensure vehicle has fuel in tank and inertia fuel shutoff switch is not tripped. Repair or replace as necessary. If no faults are found, go to next step.
  2. 2) Check Fuel Pressure  Release fuel system pressure. Turn ignition off. Install fuel pressure gauge. Locate diagnostic connector near battery. Jump Fuel Pump (FP) terminal in diagnostic connector to ground. Turn ignition on. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is zero, go to next step. If fuel pressure is lower than specified, go to step 20). If fuel pressure is higher than specified, go to step 30).
  3. 3) Check Power To Fuel Pump Relay  Turn ignition off. Remove fuel pump relay. Turn ignition on. Measure voltage on Yellow/Black wires at fuel pump relay. If battery voltage is measured, go to next step. If voltage is less than battery voltage, perform CIRCUIT TEST B . If VPWR circuit is okay, repair open Yellow/Black wire.
  4. 4) Check Fuel Pump Relay Operation  Turn ignition on. Locate diagnostic connector near battery. Jump Fuel Pump (FP) terminal at diagnostic connector to ground. See appropriate circuit schematic. If fuel pump relay clicks, go to next step. If fuel pump relay does not click, go to step 9).
  5. 5) Check Voltage To Fuel Pump  Turn ignition off. Ensure inertia fuel shutoff switch is not tripped. Disconnect fuel pump harness connector at fuel pump. Jump Fuel Pump (FP) terminal at diagnostic connector to ground. Turn ignition on. Measure voltage at fuel pump harness connector between ground and Green/Yellow wire. If voltage is 10 volts or greater, go to step 10). If voltage is less than 10 volts on Aspire, go to step 7).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 5) to step 7). No test procedures have been omitted.
    IFS SWITCH TESTING

    Switch Condition Continuity (Wire Color)
    Reset (Button Down) Green & Green
    Tripped (Button Up) No Continuity
  6. 7) Check Circuit Between Fuel Pump & Relay  Turn ignition off. Remove fuel pump relay. Disconnect harness connector at fuel pump. Measure resistance of Green/Yellow wire between fuel pump harness connector and fuel pump relay harness connector. Measure resistance between Green/Yellow wire at fuel pump harness connector and chassis ground. Resistance should be less than 5 ohms between fuel pump and relay harness connectors and greater than 10,000 ohms between circuit and ground. If resistance is as specified go to step 10). If resistance is not as specified, repair circuit wire.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 7) to step 9). No test procedures have been omitted.
  7. 9) Check Fuel Pump Relay Control Circuit  Turn ignition off. Disconnect harness connector at fuel pump. Disconnect PCM. Inspect connector for damage and repair as necessary. Install breakout box (leave PCM disconnected). Measure resistance between White/Yellow wire at fuel pump relay harness connector and breakout box test pin No. 20. If resistance is less than 5 ohms, go to CIRCUIT TEST KA . If resistance is greater than 5 ohms, repair White/Yellow wire. Restore electrical connections and repeat QUICK TEST .
  8. 10) Check Fuel Pump Ground  Turn ignition off. Disconnect harness connector at fuel pump. Measure resistance between Green wire at fuel pump harness connector and ground. If resistance is less than 5 ohms, replace fuel pump. Restore electrical connections and repeat QUICK TEST . If resistance is greater than 5 ohms, perform step 6) and return to next step.
  9. 11) Check Ground At IFS Switch  Turn ignition off. Disconnect IFS switch. Measure resistance of Black wire between IFS harness connector and ground. If resistance is greater than 5 ohms, repair Black wire. Restore electrical connections and repeat QUICK TEST . If resistance is less than 5 ohms, repair Green wire between IFS switch and fuel pump.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 20). No test procedures have been omitted.
  10. 20) Check Power Supply To Fuel Pump  Turn ignition off. Disconnect harness connector at fuel pump. Jump Fuel Pump (FP) terminal at diagnostic connector to ground. Turn ignition on. Measure voltage between ground and Green/Yellow wire at fuel pump harness connector. If voltage is 10 volts or greater, go to next step. If voltage is less than 10 volts, go to step 3).
  11. 21) Check Fuel Filter  Release fuel pressure. Remove high pressure in-line fuel filter. Replace filter or evaluate filter condition. If filter is okay, go to next step.
  12. 22) Check Pressure Regulator Diaphragm  Install fuel pressure gauge to fuel system service port. Start engine and operate for 10 seconds. Turn ignition off and wait 10 seconds. Start engine again and operate for 10 seconds. Turn ignition off. Disconnect and inspect vacuum hose from fuel pressure regulator. If hose is wet with fuel, replace fuel pressure regulator. If hose is dry, go to next step.
  13. 23) Check Pressure Regulator Leakdown  With fuel pressure gauge installed, turn ignition off. Reconnect vacuum hose to pressure regulator. Start and run engine for at least 30 seconds. Turn ignition off. If fuel pressure is greater than 21 psi (147 kPa) after engine has been off 5 minutes, go to next step. If fuel pressure drops below 21 psi, go to step 40) to check injectors. Replace injectors if necessary. If injectors are okay go to next step.
  14. 24) Check Pressure Regulator Seat Leakage  Remove fuel pressure regulator. Connect a vacuum pump to fuel return tube on pressure regulator. Apply 20 in. Hg. If vacuum maintains 10 in. Hg or greater for 10 seconds or more, pressure regulator is okay, go to next step. If vacuum drops below 10 in. Hg within 10 seconds, replace pressure regulator. Recheck fuel pressure.
  15. 25) Check Fuel Pump Volume  Install fuel pressure gauge. Place fuel pressure gauge by-pass hose in a measuring vessel. Jump Fuel Pump (FP) terminal at diagnostic connector to ground. Turn ignition on for 10 seconds. Fuel pump should deliver 5.5 oz. or more in 10 seconds. If fuel pump volume is okay, go to next step. If fuel pump volume is insufficient, replace fuel pump. Recheck fuel pressure and repeat QUICK TEST .
  16. 26) Check Fuel Pump Check Valve  Install fuel pressure gauge. Jump Fuel Pump (FP) terminal at diagnostic connector to ground. Run fuel pump for 30 seconds. Remove jumper wire. Note fuel pressure after 3 minutes. If fuel pressure drops more than 2 psi (13.7 kPa) within 3 minutes, replace fuel pump. Recheck fuel pressure and repeat QUICK TEST . If fuel pressure does not drop 2 psi (13.7 kPa) within 3 minutes, go to step 40).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 26) to step 30). No test procedures have been omitted.
  17. 30) Check Regulator For Cause Of High Pressure  Inspect fuel pressure regulator for dents that could cause higher than normal spring tension on pressure regulator valve. Remove vacuum hose from pressure regulator and inspect for fuel leakage. Replace pressure regulator if necessary. If fuel pressure regulator is okay, go to next step.
  18. 31) Check Fuel Return Line  Disconnect fuel return line at pressure regulator and at fuel tank. Blow through fuel return line with 5-10 psi (35-69 kPa) of regulated shop air. If return line is restricted, repair or replace as necessary. If line is not restricted, replace fuel pressure regulator and recheck fuel pressure.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 31) to step 40). No test procedures have been omitted.
  19. 40) Inspect Fuel Injectors  With engine idling (cranking if engine will not start) listen for a regular clicking sound from each injector using a mechanics stethoscope. If a regular clicking sound can be heard, go to step 43). If a regular clicking sound cannot be heard, go to next step.
  20. 41) Check Fuel Injector Signal  Disconnect injector. Insert fuel injector checker "noid light" into injector harness connector. Start or crank engine and observe noid light. Repeat procedure for all injectors. If all injector circuits indicate continuity, go to next step. If any injector circuit does not indicate continuity, go to CIRCUIT TEST H , step 45).
  21. 42) Check Fuel Injector Resistance  Disconnect fuel injector harness connectors. Measure resistance across terminals of each injector. If resistance of all injectors is 12-16 ohms @ 68°F (20°C), go to next step. If resistance of any injector is not 12-16 ohms @ 68°F (20°C), replace faulty injector(s) and go to next step.
  22. 43) Check Injectors For Leakage  Turn ignition off. Remove fuel rail assembly from intake manifold (leave hoses and injectors attached). Jump FP terminal in diagnostic connector to ground. Turn ignition on (do not crank engine). If any injector leaks more than one drop per 2 minutes, replace or clean leaky injector. Repeat QUICK TEST . If injectors leak less than one drop per 2 minutes, fuel delivery system is okay, see test procedures under CIRCUIT TEST Z , for intermittent diagnostics.
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