Electronic Ignition System Diagnosis

Electronic Ignition System Diagnosis

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) 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:

* An ignition voltage circuit
* A ground circuit
* An IC control circuit
* A low reference circuit

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

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

J 26792 HEI Spark Tester

Circuit/System Verification

Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications to verify the following:

* 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 (Specifications).

Circuit/System Testing

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

1. Turn OFF the ignition.
2. Inspect the fuse that supplies voltage to the ignition coil/modules.

• If the fuse is open, then test the spliced circuits and the individual ignition coil/modules for a short to ground.

3. Disconnect the affected ignition coil/module.
4. Connect a test lamp between the ignition coil/module ignition 1 voltage circuit terminal A and a good ground.
5. Turn ON the ignition.
6. With the test lamp still connected, measure for battery voltage between the ignition 1 voltage circuit and a good ground.

• If the voltage is not within 1 volt of battery voltage, repair the high resistance or the open in the ignition 1 voltage circuit.

7. Turn OFF the ignition, and all electrical accessories. Allow sufficient time for all of the control modules to power down before taking a resistance measurement.
8. Measure for a proper value of less than 5 ohms between the ground circuit terminal D of the affected ignition coil/module and a good ground.

• If the resistance is more than 5 ohms, repair the high resistance or the open in the ground circuit.

9. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
10. Start the engine and observe the scan tool.

• If the misfire transfers with the suspect ignition coil/module, replace as needed.
• If the misfire does not transfer with the suspect ignition coil/module, observe the component testing procedures below, and replace the spark plug if needed.

Component Testing

* Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection (Testing and Inspection).
* 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 - Bank 1 (Service and Repair)
* Ignition Coil Replacement - Bank 2 (Service and Repair)
* Spark Plug Replacement (Service and Repair)