Ignition System: Testing and Inspection

Electronic Ignition (EI) System Diagnosis

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* 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 (IC) circuit of each ignition coil/module to enable a spark event. Each ignition coil/module has the following circuits:

* Ignition voltage circuit
* Ground circuit
* IC circuit
* Low reference circuit

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 IC circuit can cause a misfire before DTC P0351-P0354 sets.
* Extended engine cranking time, may foul the spark plugs with excessive fuel.

Special Tools

J26792 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 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 1 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 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 ECM.

Important: If the ignition 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 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 plug/s.

Component Testing

Use the J26792 to verify the output of each ignition coil/module.

Repair Instructions

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

* Ignition Coil Replacement
* Spark Plug Replacement