Diagnostic Aids

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

Enter this CIRCUIT TEST only when all steps under QUICK TEST have been successfully completed and engine still does not start or if directed here from another test or chart. This test is only intended to diagnose:

Spark (PCM-controlled).
Wiring harness circuits (PIP, IGN GND and VPWR).
Powertrain Control Module (PCM).

To prevent replacement of good components, be aware the following non-EEC related areas and components may be cause of problem:

Fuel quality and quantity.
Ignition (general condition).
Engine mechanical components.
Starter and battery circuits.
Crankshaft Position (CKP) sensor.
Ignition Control Module (ICM).
Coil packs.

Fig 1: Ignition System Wiring Diagram (4.0L)

TEST PIN NO. 4 (IDM) WIRE COLOR IDENTIFICATION

Application	Wire Color
4.0L	Tan/Yellow

TEST PIN NO. 36 (SPOUT) WIRE COLOR IDENTIFICATION

Application	Wire Color
4.0L	Pink

TEST PIN NO. 56 (PIP) WIRE COLOR IDENTIFICATION

Application	Wire Color
4.0L	Gray/Orange

1) Starting System Ensure fuel pump Inertia Fuel Shutoff (IFS) switch is closed (button pushed in). Try to start engine. If engine does not crank, check vehicle starting and charging systems. If engine cranks, go to step 2).

2) Check VREF Signal At TP Sensor Turn ignition off. Disconnect Throttle Position (TP) sensor. Turn ignition on (engine off). Measure voltage between VREF and SIG RTN at TP sensor harness connector.See Fig 2. If voltage is not 4-6 volts, go to CIRCUIT TEST C. If voltage is 4-6 volts, reconnect TP sensor and go to next step.

Fig 2: TP Sensor Wiring Harness Connector Terminal ID (4.0L)

3) Check For Spark At Plugs Disconnect any spark plug wire. Connect spark tester between plug wire and engine ground. Crank engine and check for spark. If spark is present, reconnect spark plug wire and go to next step. If spark is not present, check ignition system. See IGNITION SYSTEMS in SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section.

4) Check IGN GND Continuity Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Disconnect Ignition Control Module (ICM). Measure resistance between test pin No. 16 breakout box and IGN GND terminal at ICM wiring harness connector. If resistance is 5 ohms or more, repair open IGN GND circuit and repeat QUICK TEST. If reading is less than 5 ohms, go to next step.

5) Check PIP For Short To Power Ensure ICM and PCM are disconnected. Turn ignition on. Measure voltage between test pin No. 56 at breakout box and negative battery terminal. If voltage is greater than 7 volts, repair PIP circuit for short to power, and repeat QUICK TEST. If voltage is 7 volts or less, go to next step.

6) Check PIP Circuit Continuity Turn ignition off. Measure resistance between test pin No. 56 at breakout box and PIP terminal at ICM wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open PIP circuit and repeat QUICK TEST.

7) Check PIP Circuit For Short To Ground Ensure ICM and PCM are disconnected. Measure resistance between test pin No. 56 (PIP) and test pins No. 16, 40, 46 and 60 for short to ground. If any reading is less than 10,000 ohms, repair shorted PIP circuit and repeat QUICK TEST. If engine still does not start, go to next step. If all readings are 10,000 ohms or more, go to next step.

8) Isolate Shorts In PCM Ensure ignition is turned off. With breakout box installed, connect PCM to breakout box. Leave ICM disconnected. Measure resistance between test pin No. 56 (PIP) and test pins No. 37 and 57 for short to power. Measure resistance between test pin No. 56 and test pins No. 40 and 60 for short to ground. If any reading is not 15,000-180,000 ohms, replace PCM and repeat QUICK TEST. If all readings are 15,000-180,000 ohms, go to next step.

9) Check PIP Signal Turn ignition off. Disconnect PCM from breakout box. Reconnect ICM wiring harness connector. Measure voltage between test pins No. 56 and 16 at breakout box while cranking engine. Record voltage. If voltage is 3-7 volts, go to next step. If voltage is not 3-7 volts, replace ICM and repeat QUICK TEST.

10) Isolate Short In PCM Turn ignition off. Reconnect PCM to breakout box, leaving ICM disconnected. Measure voltage between test pins No. 56 and 16 at breakout box while cranking engine. Record voltage. If voltage is 3-7 volts, go to next step. If voltage is not 3-7 volts, replace PCM and repeat QUICK TEST.

CAUTION: Stop this test at first sign of a fuel leak. DO NOT allow smoking or an open flame in vicinity of vehicle during these tests.

11) Fuel Pump Check Connect fuel pressure gauge to vehicle. Note initial fuel pressure reading. Pressurize fuel system by turning ignition on for one second, and observe pressure gauge. Turn ignition off, and wait 10 seconds. Repeat sequence 5 times. If pressure increases, go to CIRCUIT TEST S. If pressure does not increase, go to FUEL SYSTEM in SYSTEM/COMPONENT TESTS - EEC-IV (4.0L) article in the ENGINE PERFORMANCE section.