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Electronic Ignition System Diagnosis

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

This ignition system uses individual Ignition Coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control circuits to the individual ignition coil assemblies in firing order sequence. Each ignition coil has the following circuits:

    • An ignition voltage circuit
    • A ground circuit
    • An ignition control circuit

Diagnostic Aids
    • This test procedure requires that the vehicle battery has passed a load test and is completely charged.
    • There is an adequate supply of fuel in the fuel tank.
    • When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness.
    • Use the EL 35616-E terminal test kit for any test that requires probing the underbonnet fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.
    • A slight to moderate resistance in the ignition voltage circuit can cause a misfire condition or a crank/no start concern.
    • Extended engine cranking time, will foul the spark plugs with excessive fuel and cause a crank/no start condition.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electronic Ignition System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • EL 26792 HEI Spark Tester
    • EL 35616-E Terminal Test Kit

For equivalent regional tools, refer to Special Tools .

Circuit/System Verification

Note: Verify that the engine is in good mechanical condition before continuing with this diagnostic.

Observe the engine controls schematic for the ignition module/coils, and review the ignition system specifications to verify the following concerns:

    • The ignition modules/coils are correctly wired and connected.
    • The proper spark plug type, refer to Spark Plug Inspection .
    • The proper spark plug gap and torque.
    • The proper Ω values for the spark plug leads.

Circuit/System Testing
  1. Turn OFF the ignition.

    2. Note: If the ignition fuse F9 is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.

  2. Inspect the fuse that supplies ignition voltage to the ignition module/coils.
    3. ⇒If fuse F9 is open, test all ignition voltage circuits to the T8 Ignition Coil for a short to ground.
  3. Disconnect the T8 Ignition Coil connector.
  4. Replace the open fuse F9 with a new fuse.
  5. Ignition ON, engine OFF.
  6. Reconnect T8 Ignition Coil connector.
    7. ⇒If the fuse F9 opens when connecting the T8 Ignition Coil, then replace the T8 Ignition Coil.
  7. Ignition OFF, disconnect the T8 Ignition Coil electrical connector.
  8. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal A and ground.
    9. ⇒If the test lamp does not illuminate test the T8 Ignition Coil Ignition Voltage Circuit for an open/high resistance.
  9. Verify that a test lamp illuminates between the T8 Ignition Coil Ground Circuit terminal B and B+.
    10. ⇒If the test lamp does not illuminate, test the T8 Ignition Coil Ground Circuit for an open/high resistance.
  10. Exchange the affected T8 Ignition Coil assembly with a known good assembly.

    11. Note: An open / high resistance on the low reference circuit to the ignition control module may cause a misfire.

  11. Start and idle the engine. Observe the misfire counters on the scan tool.
    12. ⇒If the misfire or crank/no start is resolved, replace the T8 Ignition Coil/module assembly.
    ⇒If the misfire does not transfer with the suspect T8 Ignition Coil, measure the resistance of the ignition control circuit. The ignition control circuit should measure less than 5 Ω. If the circuit tests normal, replace the K20 Engine Control Module.

Component Testing

Static Test

    • Use the spark plug inspection procedure to verify the integrity of the spark plugs. Replace the spark plug if necessary.

       Note: An erratic or weak spark is considered a no spark condition.

    • Use the EL 26792 HEI spark tester to verify the output of the T8 Ignition Coil. If no spark is detected across the gap of the spark plug tester, replace the T8 Ignition Coil assembly.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ignition Coil Replacement
    •  Spark Plug Replacement
    • Control Module References for replacement, setup, and programming
   


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