Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Ranger. However, it is still accessible from the selected car via links, so may be relevant.

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.

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.

CIRCUIT TEST ACRONYMS

Acronym	Definition
DLC	Data Link Connector
PID	Parameter Identification

1) Check System Integrity

Turn ignition off. Inspect fuel system for leaks, damage or kinked 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 switch is set correctly. Repair or replace as necessary. If no faults are found, go to next step.

2) Check Fuel Pressure

Release fuel system pressure. Turn ignition off. Install fuel pressure gauge. Connect scan tester to DLC. Turn ignition on. Access scan tester Output Test Mode. Operate fuel pump at maximum fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to step 9).

3) 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 of specification for 60 seconds, go to step 5). If fuel pressure does not remain within 5 psi of specification for 60 seconds, go to next step.

4) Check Pressure Regulator Diaphragm

With fuel pressure gauge installed, 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 hose from fuel pressure regulator. If hose is wet with fuel, replace fuel pressure regulator. If hose is dry, go to step 11).

5) 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 gauge reading stays within 3 psi of original pressure reading, go to next step. If gauge reading does not stay within 3 psi of original pressure reading, go to step 8).

6) Check Fuel Pressure Regulator; Test Drive Vehicle

With fuel pressure gauge installed, reconnect fuel pressure regulator hose. Install vacuum gauge to intake manifold. Ensure both gauges can be seen by vehicle operator. Drive vehicle while noting gauges during heavy acceleration. Gauge readings should be as follows:

Fuel pressure gauge reading increases and vacuum gauge reading decreases.
Fuel pressure gauge reading decreases and vacuum gauge reading increases.

If gauge readings are correct, fuel system is okay and testing is complete. If gauge readings are not correct, go to next step.

7) Check Vacuum Supply

Turn ignition off. Disconnect and plug fuel pressure regulator 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, system is okay and testing is complete. If fuel pressure does not change as vacuum changes, replace fuel pressure regulator.

8) Check Fuel Filter

Turn ignition off. Connect scan tester to DLC. Replace fuel filter. Turn ignition on. Enter Output Test Mode (OTM) and operate fuel pump. Compare fuel pressure gauge readings. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, system is okay. Return to step 3). If fuel pressure is not as specified, go to step 12).

9) Check Fuel Pressure Regulator

Leave ignition off and scan tester connected to DLC. Release fuel system pressure. Disconnect fuel hose at fuel rail. Connect hose to fuel rail and put opposite end of hose in clean, one quart container. Turn ignition on. Enter Output Test Mode (OTM) to turn fuel pump on. Note fuel pressure and fuel returning to container. Exit OTM to turn fuel pump off. If fuel pressure is 35-40 psi with fuel returning to container, go to next step. If fuel pressure is not 35-40 psi with fuel returning to container, replace fuel pressure regulator.

10) Check Fuel Return System

Turn ignition off. Release fuel system pressure. Disconnect fuel hose at fuel pressure regulator. Check fuel return system for kinked or restricted hoses. Disconnect fuel return hose near fuel tank. Apply 3-5 psi to fuel hose from pressure regulator side. If air flows freely, replace fuel pump. If air does not flow freely, repair or replace hose as necessary.

11) Check Fuel Injector Flow & Leakage

Turn ignition off. Use Rotunda Injector Tester (113-00001) to flow test fuel injectors. If flow rate for each fuel injector is within specification, system is okay and testing is complete. If flow rate for any fuel injector is not within specification, replace defective fuel injector and repeat QUICK TEST .

12) Check Fuel Pump Voltage

Turn ignition off. Ensure scan tester is connected to DLC. Disconnect fuel pump wiring harness connector. Check connector terminals for damage and repair as necessary. Enter Output Test Mode (OTM) and activate fuel pump circuit. Check voltage at fuel pump connector. If voltage is 10.5 volts or more, check fuel pump ground connection. Repair as necessary. If ground connector is okay, replace fuel pump. If voltage is less than 10.5 volts, isolate source of low voltage and repair as necessary.