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Diagnostic Aids

WARNING: This page is about a different variant/trim than selected.

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:

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

Fig 1: Ignition System Test Circuits
G95A35923
  1. 1) Starting System Check  Ensure fuel pump inertia 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 next step.
  2. 2)  Attempt to start engine. If engine now starts, go to CIRCUIT TEST Z, step 50). If engine does not start, go to next step.
  3. 3) Check For Malfunction Indicator Light (MIL) During Cranking  Turn ignition off. Turn ignition on and observe MIL. If MIL is off, go to CIRCUIT TEST NB, step 1). If MIL is on, turn ignition switch to the START position. If MIL goes off, PIP circuit is okay; go to next step. If MIL stays on while engine is cranking, go to step 6).
  4. 4) Check VREF At TP Sensor  Turn ignition off. Disconnect TP sensor. Measure voltage between terminal VREF and SIG RTN at TP sensor wiring harness connector. See Figure. If voltage is 4-6 volts, go to step 7). If resistance not 4-6 volts, go to CIRCUIT TEST C.
  5. 5) Check Flash EPROM (FEPS) Circuit For Short To Power  With ignition on, measure voltage between negative battery terminal and DLC terminal No. 13. See Figure. If voltage is less than 9 volts, go to next step. If voltage is 9 volts or more, repair circuit for a short to power and repeat quick test.
  6. 6) Check For Spark At Plugs  Disconnect any spark plug wire. Connect spark tester between spark plug wire and ground. Connect Spark Plug Firing Indicator (D89P-6666-A). Crank engine while checking for spark. If spark is okay go to next step. If spark is not okay, go to CIRCUIT TEST JD, step 1).
  7. 7) Check Fuel Pressure  Turn ignition off. Release fuel pressure. Install fuel pressure gauge. With scan tester connected, turn ignition on. Using scan tester, access OUTPUT TEST MODE and operate fuel pump to obtain max. fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, go to CIRCUIT TEST HC, step 1).
  8. 8) Check Fuel Pressure Leakdown  Leave fuel pressure gauge installed and ignition on. Turn ignition on. Using scan tester, access OUTPUT TEST MODE and operate fuel pump to obtain maximum fuel pressure. Exit OUTPUT TEST MODE and turn ignition off. If fuel pressure remains within 5 psi of maximum pressure for one minute after turning ignition off, go to next step. If fuel pressure does not remain as specified, go to CIRCUIT TEST HC, step 1).
  9. 9) Check Continuity Of Ignition Ground Circuit  Ensure ignition is turned off. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950) leaving PCM disconnected. Install EI Diagnostic Harness (007-00059) to breakout box. Connect ICM tee in-line with wiring harness. Install ICM overlay. Measure resistance between test pin No. 23 at breakout box and IGN GND terminal at the EI Diagnostic Harness. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST .
  10. 10) Check Continuity Of PIP Circuit  Ensure ignition is off and PCM is disconnected. Disconnect ICM from wiring harness. Measure resistance between test pin No. 49 at breakout and PIP circuit at EI Diagnostic Harness. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST .
  11. 11) Check PIP Circuit For Short To Power  Turn ignition on. Leave PCM and ICM disconnected. Measure voltage between test pin No. 49 and negative battery terminal. If voltage is less than one volt, go to next step. If voltage one volt or more, repair short to power and repeat QUICK TEST .
  12. 12) Check PIP Circuit For Short To Ground  Turn ignition off. Measure resistance between breakout box test pin No. 49 and test pins No. 23, 51, 91 and 103. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST . If vehicle will not start, go to next step.
  13. 13) Check PIP Signal  Ensure ignition is off. Reconnect ICM. While cranking engine, measure voltage between test pins No. 23 and 49 at breakout box. If voltage is 3-7 volts, replace PCM and repeat QUICK TEST . If voltage is not 3-7 volts, replace ICM and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 13) to step 17). No test procedures have been omitted.
  14. 17) Check PCM Driver To Coils  Turn ignition off. Connect 12-volt test light between B+ and coil driver circuit. Crank engine while observing test light. Repeat procedure for each coil driver. Test light should blink brightly, once for each engine revolution. If test light blinks as specified, replace PCM and repeat QUICK TEST . If test light does not blink as specified, go to CIRCUIT TEST JD, step 4).
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 17) to step 20). No test procedures have been omitted.
  15. 20) Identify Type Of No-Start  Attempt to start engine. If it now starts, see CIRCUIT TEST Z step 50). If engine does not start, go to next step.
    NOTE: Ensure fuel pump inertia switch is closed (button pushed in).
  16. 21) Starting System Check  Try to start engine. If engine cranks, go to next step. If engine does not crank, check vehicle starting and charging systems.
  17. 22) Check VREF At TP Sensor  Turn ignition off. Disconnect TP sensor. Measure resistance between terminal VREF and SIG RTN at TP sensor wiring harness connector. If resistance is 4-6 volts, go to next step. If resistance is not 4-6 volts, go to CIRCUIT TEST C.
  18. 23) Check For Spark At Plugs  Disconnect any spark plug wire. Connect spark tester between spark plug wire and ground. Crank engine while checking for spark. If spark is okay, go to step 33). If spark is not okay, go to next step.
  19. 24) Check For Spark At Coil  Disconnect coil secondary wire from distributor. Connect spark tester between wire and ground. Crank engine while checking for spark. If spark is okay, go to CIRCUIT TEST JB, step 1). If spark is not okay, go to next step.
  20. 25) Check Continuity Of IGN GND Circuit  Ensure ignition is turned off. Disconnect Camshaft Position (CMP) sensor. Disconnect PCM 104-pin connector and inspect for damage. Repair as necessary. Install Breakout Box (014-00950) leaving PCM disconnected. Install EI Diagnostic Harness (007-00059) to breakout box. Connect B- to negative battery terminal. Connect ICM tee and CMP tee in-line with wiring harness. Ensure PIP OPEN/NORMAL/SPOUT OPEN switch or diagnostic is in NORMAL position. Install DI overlay. Measure resistance between test pin No. 23 and 35 (IGN GND) at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST .
  21. 26)  Reconnect CMP sensor. Connect PCM to breakout box. Turn breakout box timing switch to DIST position. Try to start engine. If engine starts, go to step 31). If engine does not start, go to next step.
  22. 27) Check SPOUT Signal  Ensure ignition is off. While cranking engine, measure AC voltage between test pin No. 50 (SPOUT) and negative battery terminal. If voltage is 3-6 volts, go to CIRCUIT TEST JD. If voltage is not 3-6 volts, place timing switch in COMPUTED position and go to next step.
  23. 28) Check PIP & SPOUT Circuit For Short To Power  Turn ignition off. Disconnect CMP, ICM and PCM. Turn ignition on. Measure voltage between test pin No. 49 (PIP) and negative battery terminal. Measure voltage between test pin No. 50 (SPOUT) and negative battery terminal. If voltage is less than 10.5 volts, go to next step. If voltage 10.5 volts or more, repair short to power and repeat QUICK TEST .
  24. 29) Check PIP & SPOUT Circuit For Short To Ground  Turn ignition off. Measure resistance between breakout box test pin No. 49 (PIP) and test pins No. 23, 51, 91 and 103. Measure resistance between breakout box test pin No. 50 (SPOUT) and test pins No. 23, 51, 91 and 103. If resistance each is greater than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short circuit and repeat QUICK TEST . If vehicle will not start, go to next step.
  25. 30) Isolate Shorts In PCM  Ensure ignition is off. Connect PCM to breakout box. Measure resistance between breakout box test pin No. 49 (PIP) and test pins No. 71 and 97 for short to power. Measure resistance between breakout box test pin No. 49 (PIP) and test pins No. 51 and 103 for short to ground. Measure resistance between breakout box test pin No. 50 (SPOUT) and test pins No. 71 and 97 for short to power. Measure resistance between breakout box test pin No. 49 (PIP) and test pins No. 51 and 103 for short to ground. If resistance each is greater than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, replace PCM and repeat QUICK TEST .
  26. 31) Check PIP Signal  Ensure ignition is off and PCM is connected to breakout box. While cranking engine, measure voltage between test pin No. 49 and test pins No. 51 and 103. If voltage is 3-7 volts, replace PCM and repeat QUICK TEST . If voltage is not 3-7 volts, go to next step.
  27. 32) Check Continuity Of PIP Circuit  Ensure ignition is off. Disconnect PCM from breakout box. Disconnect CMP and ICM. Measure resistance between breakout box test pin No. 49 and EI Diagnostic Harness test pins No. 15 and 34. If resistance is less than 5 ohms, reconnect all components and go to CIRCUIT TEST JB. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST .
  28. 33) Check SPOUT Signal  Ensure ignition is off. Connect PCM to breakout box. Ensure breakout box timing switch is in COMPUTED position. While cranking engine, measure voltage between test pin No. 50 and test pins No. 51 and 103. If voltage is 3-6 volts, go to next step. If voltage is not 3-6 volts, go to step 28).
  29. 34) Check Fuel Pressure  Turn ignition off. Release fuel pressure. Install fuel pressure gauge. With scan tester connected, turn ignition on. Using scan tester, access OUTPUT TEST MODE and operate fuel pump to obtain maximum fuel pressure. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, see CIRCUIT TEST HC, step 1).
  30. 35) Check Fuel Pressure Leakdown  Leave fuel pressure gauge installed and ignition on. Turn ignition on. Using scan tester, access OUTPUT TEST MODE and operate fuel pump to obtain maximum fuel pressure. Exit OUTPUT TEST MODE and turn ignition off. If fuel pressure remains within 5 psi of maximum pressure for one minute after turning ignition off, fuel system is okay and testing is complete. If fuel pressure does not remain as specified, go to CIRCUIT TEST HC, step 1).
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