Diagnostic Aids

Enter this CIRCUIT TEST only when steps in QUICK TEST have been successfully completed but engine still does not start or if directed here from another test or chart.

This test is only intended to diagnose the following EEC-IV ignition systems and circuits:

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

Fig 1: ICM Circuit & Connector Term. ID (Exc. Aerostar & Ranger 3.0L)

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 system condition).
• Engine mechanical components.
• Starter and battery circuits.
• Distributor.
• Camshaft Position (CMP) sensor.
• Ignition Control Module (ICM).
• Ignition coil.

1. 1) Starting System  Try to start engine. If engine does not crank, check vehicle starting and charging systems. If engine cranks, verify Inertia Fuel Shutoff (IFS) switch button is pushed in. If IFS switch button is pushed in, go to step 2).
2. 2) Check VREF Signal At TP Sensor  Turn ignition off. Disconnect Throttle Position (TP) sensor. Turn ignition on (engine off). Measure voltage at TP sensor harness connector between VREF and SIG RTN.See Fig 2. If voltage is 4-6 volts, reconnect TP sensor and go to step 3). If voltage is not 4-6 volts, go to CIRCUIT TEST C.
   Fig 2: Identifying TP Sensor Wiring Harness Connector Terminals

   
3. 3) Check For Spark At Plugs  Disconnect any spark plug wire. Connect spark tester between spark plug wire and ground. Crank engine and check for spark. If spark is present and consistent, connect spark plug wire and go to step 13). If spark does not exist, connect spark plug wire and go to step 4).
4. 4) Check For Spark At Coil  Remove high-tension coil wire from distributor. Install spark tester. Check for spark while cranking engine. If spark exists, connect coil wire, and service ignition secondary system. If no spark exists, connect coil wire and go to step 5).
5. 5) Check Ignition Circuit Ground Continuity  Turn ignition off. Wait 10 seconds. Disconnect and inspect PCM 60-pin connector. Install Break-out Box (T83L-50-EEC-IV), leaving PCM disconnected. Disconnect ICM. Disconnect Hall sensor or Crank Angle Sensor (CAS) if equipped. Measure resistance between test pin No. 16 at breakout box and IGN GND circuit of Camshaft Position (CMP) sensor wiring harness connector. If reading is more than 5 ohms, repair open in IGN GND circuit and repeat QUICK TEST. If reading is 5 ohms or less, go to step 6).
6. 6) Isolate SPOUT Circuit Fault  Connect ICM, CAS or distributor hall connector as applicable. Connect PCM to breakout box. Set breakout box timing switch to DIST position. Try to start vehicle. If vehicle starts, go to step 11). If vehicle does not start, go to step 7).
7. 7) Check SPOUT Signal  Turn ignition off. Move breakout box timing switch to DIST position. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between test pin No. 36 at breakout box and negative battery terminal while cranking engine. If voltage is 3-6 volts, EEC-IV system is not at fault. Diagnose ignition system. See IGNITION SYSTEM in I - GAS SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. If voltage is not 3-6 volts, go to step 8).
8. 8) Check SPOUT & PIP Circuits For Short Circuit  Turn ignition off. With breakout box installed, move timing switch to COMPUTED position. Disconnect distributor connector. Disconnect PCM. Turn ignition on. Measure voltage between test pin No. 36 (SPOUT) and negative battery terminal. Measure voltage between test pin No. 56 (PIP) and negative battery terminal. If voltage is more than 10.5 volts, repair circuit for a short to power and repeat QUICK TEST. If engine still does not start or if all voltages are 10.5 volts or less, go to step 9).
9. 9)  Turn ignition off. Disconnect distributor connector. Measure resistance between test pin No. 36 (SPOUT) and test pins No. 16, 20, 40, 46 and 60 for short to ground. Measure resistance between test pin No. 36 and test pin No. 56 for short to PIP. Measure resistance between test pin No. 56 (PIP) and test pins No. 16, 20, 40, 46 and 60. If all readings are 10,000 ohms or more, go to step 10). If any reading is less than 10,000 ohms, repair short in harness and repeat QUICK TEST. If engine still does not start, go to step 10).
10. 10) Isolate Shorts In PCM  Turn ignition off. With breakout box installed, reconnect PCM. Measure resistance between test pin No. 36 (SPOUT) and test pins No. 37, 40, 57 and 60. Measure resistance between test pin No. 56 (PIP) and test pins No. 37, 40, 57 and 60. If any reading is less than 500 ohms, replace PCM and repeat QUICK TEST. If all readings are 500 ohms or more, ensure all components are connected and go to step 11).
11. 11) Check PIP Signal  Turn ignition off. Set DVOM on 20-volt scale. With breakout box installed, move timing switch to COMPUTED position. While cranking engine, measure voltage between test pin No. 56 (PIP) and test pins No. 40 and 60. If voltage is 3-7 volts, replace PCM. Repeat QUICK TEST. If voltage is not 3-7 volts, go to step 12).
12. 12) Check Continuity Of PIP Circuit  Turn ignition off. Disconnect PCM from breakout box. Disconnect distributor connector. Measure resistance between test pin No. 56 and distributor or ICM connector PIP circuit. If resistance is 5 ohms or more, repair open PIP circuit and repeat QUICK TEST. If resistance is less than 5 ohms, remove breakout box and diagnose ignition system. See IGNITION SYSTEM in I - GAS SYS/COMP TESTS article in the ENGINE PERFORMANCE Section.
13. 13) Verify SPOUT Signal  If spark was present in step 3), turn ignition off. Disconnect PCM 60-pin connector. Inspect for damaged pins and repair as necessary. Install breakout box, and connect PCM. Ensure breakout box timing switch is in COMPUTED position. Set DVOM on 20-volt scale. Measure voltage between test pin No. 36 and pins No. 40 and 60 while cranking engine. If voltage is 3-6 volts, go to step 20). If voltage is not 3-6 volts, return to step 8).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 13) to step 20). No test procedures have been omitted.