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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 provides 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 (IC) circuit of each ignition coil/module to enable a spark event. Each ignition coil/module has the following circuits:

* Ignition voltage
* Ground
* IC
* Low reference

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 on the circuit will pinpoint this condition.
* A slight to moderate resistance on any IC 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 End Views By Name
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 Verification

1. Verify that the engine is in good mechanical condition before continuing with this diagnostic.
2. Verify the following conditions:

* The ignition coil/modules are correctly connected
* The proper firing order
* The proper spark plug type
* The proper spark plug gap and torque
Refer to Ignition System Specifications Application and ID and Spark Plug Inspection Testing and Inspection.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the affected ignition coil/modules.
2. Ignition OFF for 90 seconds, test for less than 5 ohms between the ground circuit terminal A and ground.

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

3. Test for less than 5 ohms between the low reference circuit terminal B 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 ECM.

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


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

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

5. Exchange the affected ignition coil/module with the 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 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 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