Ignition System: Testing and Inspection

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:

* 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. To pinpoint this condition perform a voltage drop test on the circuit.
* A slight to moderate resistance on any IC 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 (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

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 (Specifications) and Spark Plug Inspection (Testing and Inspection).

Circuit/System Testing

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

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

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

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

4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 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 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 plugs.

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)