Electronic Ignition (EI) System Diagnosis

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 provides an overview of each diagnostic category.

Circuit/System Description

This ignition system uses individual ignition module/coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control (IC) circuits to the individual ignition module/coil assemblies in firing order sequence. Each ignition module/coil has the following circuits:

* An ignition 1 voltage circuit
* A ground circuit
* An IC circuit
* A low reference circuit

Diagnostic Aids

* This test procedure requires that the vehicle battery has passed a load test and is completely charged.
* There is an adequate supply of fuel in the fuel tank.
* When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness.
* Use the J 35616 for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.

Special Tools

* J 26792 Spark Plug Tester
* J 35616-A/BT-8637 Connector Test Adapter Kit

Circuit/System Verification

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

* The ignition modules/coils are correctly wired and connected
* The proper spark plug type
* The proper spark plug gap and torque
* The proper ohm values for the spark plug wires
Refer to Ignition System Specifications.

Circuit/System Testing

1. Turn OFF the ignition.

Important: This engine application uses 2 fuses, one for each bank, to supply ignition 1 voltage to the ignition module/coil assemblies and also to the fuel injectors. A good indication that a fuse is open is that all 4 misfire counters are incrementing on one side of the engine

2. Inspect both fuses that supply ignition voltage to the ignition module/coils.

^ If a fuse is open, test all 8 ignition voltage circuits to the ignition module/coils or the fuel injectors on that engine bank, for a short to ground.

3. Disconnect the 4 ignition module/coil, and the 4 fuel injector electrical connectors, for the engine bank that has the open fuse.
4. Replace the open fuse with a new fuse.
5. Ignition ON, engine OFF.
6. Reconnect each ignition module/coil, and fuel injector electrical connectors, one at a time.

^ If the fuse opens when connecting an ignition module/coil or fuel injector electrical connector, then replace the component that caused the fuse to open.

7. Ignition OFF, disconnect the appropriate ignition module/coil electrical connector.
8. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit and ground.

^ If the test lamp does not illuminate test the ignition voltage circuit for an open/high resistance.

9. Verify that a test lamp illuminates between the ignition module/coil ground circuit and B+.

^ If the test lamp does not illuminate, test the ignition module/coil ground circuit for an open/high resistance.

10. Inspect and measure the resistance of the spark plug wire.

^ If the resistance value is not within the specified range, or does not pass the inspection, replace the spark plug wire.

11. Exchange the misfiring cylinder, ignition module/coil assembly with the ignition module/coil assembly from a non-misfiring cylinder.
12. Start and idle the engine. Observe the misfire counters on the scan tool.

^ If the misfire transfers with the suspect ignition module/coil, then replace the ignition module/coil assembly.
^ If the misfire does not transfer with the suspect ignition module/coil, then measure the resistance of the IC circuit. The IC circuit should measure less than 5 ohms. If the circuit tests normal, replace the ECM.

Component Testing

* Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to Spark Plug Inspection. Replace the spark plug if necessary. Testing and Inspection

Important: An erratic or weak spark is considered a no spark condition.

* Use the J 26792 to verify the output of each ignition module/coil. If no spark is detected across the gap of the spark plug tester, then replace the ignition module/coil assembly.

Repair Instructions

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

* Engine Control Module Programming and Setup
* Engine Control Module Replacement
* Ignition Coil Replacement
* Spark Plug Replacement