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Home >> Ford >> 1989 >> Bronco II 4WD, Standard, M5OD-R1 >> Repair and Diagnosis >> Engine Performance >> System >> 2.9L CEC Tests W/Codes >> Circuit Test >> Test D12 - IDM
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Test D12 - IDM

NOTE: Perform this test when Service Code 14, 18, 19, 28, 45, 46, 48 or 88 is displayed during QUICK TESTS or when directed here by other test procedures.
Fig 1: 2.9L TFI IDM Circuit
G120763

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault:

This test is intended to diagnose the following circuits and components: Harness circuits: IGNITION GROUND, SPOUT, PIP, IDM & DPI and ECA assembly.

Vehicles with 2.9L engines use the TFI ignition system. The TFI module is mounted in the distributor and a single module connector is used.

  1. Code 14: Erratic Ignition. Code 14 indicates two successive erratic Profile Ignition Pickup (PIP) pulses occurred, resulting in a possible engine miss or stall. Possible causes for this fault are: loose wires or connectors, arcing secondary ignition components or on-board transmitter equipment (2-way radio). If any of the above are present, service as necessary, clear code and rerun QUICK TEST. If the items listed are not present, go to step 3).
  2. Check For Other Codes. If Codes 45, 46 or 48 are present, go to step 12). If Codes 45, 46 or 48 are not present, go to next step.
  3. Continuous Memory Codes 14, 18, 28 or 48: Check IDM Circuit Continuity.

    Code 18 indicates a loss of IDM input signal. Possible causes:

    • Open harness circuit
    • Shorted harness
    • Faulty TFI module
    • Faulty ECA

    Code 28 indicates IDM input signal always low. Possible causes:

    • Open or shorted harness
    • Faulty CID sensor
    • VBAT (battery voltage) low at DIS
    • Faulty ECA

    Code 48 indicates IDM input signal always high. Possible causes:

    • Open signal in harness
    • VBAT open at secondary coil
    • VBAT low at secondary coil

    NOTE: On TFI vehicles, the IDM circuit has a 22K-ohm resistor between test pin No. 4 and the ignition coil negative terminal.

    Turn key off and wait 10 seconds. Disconnect E-core ignition coil. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leave ECA connected and set DVOM on 200K-ohm scale. On TFI equipped vehicles, measure resistance between test pin No. 4 at the breakout box and negative terminal of ignition coil harness connector. If resistance is between 20K and 24K ohms, go to next step. If resistance is not to specification, repair open circuit, clear codes, retest and reconnect E-core coil.

  4. Checking IDM Circuit For Short to Ground. Turn key off and wait 10 seconds. Disconnect E-core ignition coil on TFI vehicles. Install breakout box and ECA disconnected. With DVOM on 200K-ohm scale, measure resistance between test pin No. 4 and test pins No. 40, 46, and 60. If any reading is less than 10K ohms, repair short to ground in IDM circuit, reconnect all components and rerun QUICK TEST. If all readings are 10K ohms or more, reconnect components and go to next step.
  5. Checking ECA For Short to Ground. Turn key off and wait 10 seconds. Disconnect E-core ignition coil. Install breakout box and connect ECA. With DVOM on 200K-ohm scale, measure resistance between test pin No. 4 and test pins No. 40, 46, and 60. If any reading is less than 10K ohms, replace ECA, reconnect all components and rerun QUICK TEST. If all readings are 10K ohms or more, reconnect components and go to next step.
  6. Checking Ignition Module. Turn key off and wait 10 seconds. Deactivate SELF-TEST. Using CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault while lightly tapping on TFI module to simulate road shock. Wiggle TFI harness connectors. On Closed Bowl Distributor (CBD) models, wiggle TFI and distributor hall connectors. If fault is indicated, disconnect and inspect TFI harness connectors and terminals for damage. If connector and terminals are okay, check TFI ignition system, if ignition is okay, replace ECA. If no fault is indicated, go to next step.
  7. Checking EEC-IV Harness. While in CONTINUOUS MONITOR (WIGGLE) TEST, observe VOM or diagnostic tester for indication of fault while wiggling, shaking, or bending small sections of harness while working from TFI connector toward firewall. Repeat process from firewall to ECA. On CBD systems also test distributor Hall connector. Perform this test to check for faults in the following circuits:
    • PIP Open/Shorted to Ground. Check circuit at test pin No. 56.
    • SPOUT Shorted to Ground. Check circuit at test pin No. 36.
    • Ignition Ground Open. Check circuit at test pin No. 16.
    • IDM Open to Ground. Check circuit at test pin No. 4.
    • IDM Shorted to Power. Check circuit at test pin No. 4.

    Perform CONTINUOUS MONITOR (WIGGLE) TEST on these circuits one at a time in order to isolate fault. If fault is indicated, isolate fault and repair harness. Repeat QUICK TEST. If no fault is indicated, go to next step.

  8. Checking ECA and Harness Connectors. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion or loose wires. If connector is damaged, repair as necessary, clear codes and repeat QUICK TEST. If connector is okay, perform the following procedure based on the Continuous Memory Code displayed:
    • Code 14  - Unable to duplicate erratic ignition fault in EEC system. Remove breakout box, reconnect all components.
    • Code 18  - Replace ECA, remove breakout box and reconnect all components. Start and run engine for about one minute and rerun QUICK TEST.
    • Codes 28 and 48  - Remove breakout box and reconnect all components. Diagnose ignition system. If ignition system is okay, replace ECA.
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