Diagnostic Aids

Perform this test when directed by QUICK TEST or if directed by other test procedures. This test is used to diagnose:

• Fuel pressure.
• Fuel filter.
• Fuel return.
• Fuel supply.
• Fuel injector.
• Engine vacuum systems.
• Chassis components.

1. Check System Integrity
   
   Turn ignition off. Inspect fuel system for leaks, damage or kinked hoses. Inspect fuel system related wiring harness connectors for loose, damaged or corroded terminals. Repair as necessary. Ensure Inertia Fuel Shutoff (IFS) switch is set (reset button in down position). Ensure battery is fully charged and fuses are okay. Repair as necessary. If no faults are found, go to next step.
2. Check Voltage At Fuel Pump Connector
   
   Connect battery charger to battery. Ensure vehicle has fuel in tank. Disconnect fuel pump connector. Turn ignition on. Connect DVOM between fuel pump power circuit terminal and ground terminal at fuel pump wiring harness connector. See appropriate wiring diagram in WIRING DIAGRAMS article. Using scan tool, access OUTPUT TEST MODE. Command fuel pump ON and observe DVOM voltage reading. If voltage is more than 12.5 volts, exit output test mode. Reconnect fuel pump connector and go to next step. If voltage is 12.5 volts or less, go to TEST KB, step 70)  (vehicles with electronic returnless fuel systems) or check for open or short circuits in fuel pump power circuit (all other models). See FUEL SYSTEM IDENTIFICATION  table.
   FUEL SYSTEM IDENTIFICATION
   
   

   Application	Fuel System
   Continental, Escort & Tracer	Electronic Returnless
   Ranger	Mechanical Returnless
   All Others	(1) Returnable
   (1) Fuel is returned to fuel tank by means of return line from fuel rail.

3. Check For Proper Fuel Filter Maintenance
   
   Check last time fuel filter was replaced. If fuel filter has been serviced regularly (within 30,000 miles), go to next step. If fuel filter has not been serviced regularly, replace fuel filter and go to next step.
4. Check Fuel Pressure
   
   Release fuel system pressure. Turn ignition off. Install fuel pressure gauge. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. Command fuel pump ON. Note fuel pressure. See FUEL PRESSURE SPECIFICATIONS . On models with returnable fuel system, if fuel pressure is as specified, go to next step. On models with electronic/mechanical returnless fuel system, if fuel pressure is as specified, go to step  12. See FUEL SYSTEM IDENTIFICATION  table. If fuel pressure is not as specified, proceed as follows:
   • On Ranger, if fuel pressure is more than 65 psi (448 kPa), replace fuel pressure regulator in fuel tank. Recheck fuel pressure. If fuel pressure is less than 45 psi (310 kPa), go to next step.
   • On models with electronic returnless fuel system, if fuel pressure is less than 75 psi (517), go to step  13. If fuel pressure is more than 85 psi (586 kPa), no problem is indicated at this time. Check for additional symptoms and repair as necessary. See TROUBLE SHOOTING - NO CODES - EEC-V article.
   • On all other models, if fuel pressure is not as specified, proceed as follows. On Contour, Cougar and Mystique, if fuel pressure is more than 40 psi (280 kPa), go to step  10. If fuel pressure is less than 35 psi (240 kPa), go to step  13. On all models except Contour, Cougar and Mystique, if fuel pressure is more than 60 psi (415 kPa), go to step  10. If fuel pressure is less than 45 (310 kPa), go to step  13.
5. Check System Ability To Hold Fuel Pressure
   
   With fuel pressure gauge installed, turn ignition off. Exit OUTPUT TEST MODE. If fuel pressure remains within 5 psi (34 kPa) of specification for 60 seconds, go to step  7. If fuel pressure does not remain within 5 psi (34 kPa) of specification for 60 seconds, go to next step.
6. Check Pressure Regulator Or Pulse Damper Diaphragm
   
   With fuel pressure gauge installed, start engine and operate for 10 seconds. Turn ignition off and wait 10 seconds. Start engine again and allow to idle for 10 seconds. Turn ignition off. Disconnect and inspect vacuum hose from fuel pressure regulator or pulse damper. If hose is wet with fuel, replace fuel pressure regulator or pulse damper. If hose is dry, go to step  13 (Ranger) or go to step  12 (all other models).
7. Check Fuel Pressure; Test Drive Vehicle
   
   With fuel pressure gauge installed, disconnect and plug fuel pressure regulator hose. Ensure fuel pressure gauge can be seen by vehicle operator. Drive vehicle while noting gauge reading during heavy acceleration. If fuel pressure reading stays within 3 psi (21 kPa) of original pressure reading, go to next step. If fuel gauge reading does not stay within 3 psi (21 kPa) of original pressure reading, go to step  13.
8. Check Fuel Pressure Regulator; Test Drive Vehicle
   
   With fuel pressure gauge installed, reconnect fuel pressure regulator vacuum hose. Install vacuum gauge to intake manifold. Ensure both gauges can be seen by vehicle operator. Drive vehicle while noting gauge values during heavy acceleration. Gauge readings should be as follows:
   • Fuel pressure gauge reading increases as vacuum gauge reading decreases.
   • Fuel pressure gauge reading decreases as vacuum gauge reading increases.

   If gauge readings are as specified, fuel system is functioning properly and testing is complete. If gauge readings are not as specified, go to next step.

9. Check Vacuum Supply
   
   Turn ignition off. Disconnect and plug fuel pressure regulator vacuum hose. Install vacuum pump to fuel pressure regulator. Start engine and operate at idle. Observe fuel pressure gauge while applying vacuum to regulator. If fuel pressure changes as vacuum changes, repair vacuum source to fuel pressure regulator. If fuel pressure does not change as vacuum changes, replace fuel pressure regulator.
10. Check Fuel Pressure Regulator
    
    Leave ignition off and scan tool connected to DLC. Release fuel system pressure. Disconnect fuel return hose at fuel rail. Connect a separate hose to fuel rail and put opposite end of hose in clean, one quart container. Turn ignition on. Enter OUTPUT TEST MODE. Command fuel pump ON. Note fuel pressure and fuel returning to container. Exit OUTPUT TEST MODE. Command fuel pump OFF. On Contour 2.5L, Cougar 2.5L and Mystique 2.5L, if fuel pressure is 45-60 psi (310-415 kPa) with fuel returning to container, go to next step. If fuel pressure is not 45-60 psi (310-415 kPa) or fuel is not returning to container, replace fuel pressure regulator. On all models except Contour 2.5L, Cougar 2.5L and Mystique 2.5L, if fuel pressure is 35-40 psi (240-280 kPa) with fuel returning to container, go to next step. If fuel pressure is not 35-40 psi (240-280 kPa) or fuel is not returning to container, replace fuel pressure regulator.
11. Check Fuel Return
    
    Ensure fuel return line is disconnected at fuel rail. Disconnect fuel return hose at fuel pump. Check return hose for restrictions. Apply 3-5 psi (21-34 kPa) compressed air to return hose. If air flows freely, replace fuel pump. If air does not flow freely, repair or replace fuel return hose.
12. Check Fuel Injector Flow & Leakage
    
    Turn ignition off. Use Rotunda fuel injector tester from Fuel Tester Kit (113-00114) to flow test fuel injectors. If flow rate for any fuel injector is not within specification, replace defective fuel injector. If flow rate for each fuel injector is within specification, proceed as follows. On models with electronic/mechanical fuel systems, check for additional symptoms and repair as necessary. See TROUBLE SHOOTING - NO CODES - EEC-V article. On models with returnable fuel system, replace fuel pump.
13. Check Fuel Supply System
    
    Turn ignition off. Release fuel system pressure. Disconnect fuel supply hose at fuel rail and at the fuel pump. Check supply hose for restrictions. Apply 3-5 psi (21-34 kPa) compressed air to supply hose. If air flows freely, replace fuel pump. If air does not flow freely, repair or replace fuel supply hose.