Ignition System: Testing and Inspection

Electronic Ignition System Diagnosis

Diagnostic Instructions

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

Circuit/System Description

The ignition system uses individual ignition coil/module assemblies for each cylinder. The engine control module (ECM) controls the individual coils by transmitting timing pulses on the ignition control circuit of each ignition coil/module to enable a spark event.

Diagnostic Aids

* Depending on location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start concern. A voltage drop test will pinpoint this condition.
* A slight to moderate resistance on any ignition control circuit can cause a misfire before DTC P0351-P0354 sets.
* Extended engine cranking time, may foul the spark plugs with excessive fuel.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information
Special Tools

J 26792 - HEI Spark Tester

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the affected T8 ignition coil/modules.
2. Ignition OFF, all vehicle systems OFF. This may take up to 2 minutes. Test for less than 5 ohm between the ground circuit terminal A/1 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Test for less than 5 ohm between the low reference circuit terminal B/2 and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal D/4 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

5. Exchange the affected T8 ignition coil/module with the T8 ignition coil/module of a good cylinder.
6. Start the engine, and observe the scan tool Misfire Current Cylinder parameters.

• If the misfire transfers with the suspect T8 ignition coil/module, replace as needed.

7. If the circuits test normal, test or replace the spark plug/s.

Component Testing

Use the J 26792 - Spark Tester to verify the output of each ignition coil/module.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Ignition Coil Replacement (Service and Repair)
* Spark Plug Replacement (Service and Repair)