Ignition System: Testing and Inspection

ELECTRONIC IGNITION (EI) SYSTEM DIAGNOSIS

DIAGNOSTIC INSTRUCTIONS
- Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
- Strategy Based Diagnosis for an overview of the diagnostic approach.
- Diagnostic Procedure Instructions provide 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.

CIRCUIT/SYSTEM VERIFICATION
Observe the Computers and Control Systems 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.

2. 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

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 the 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.
- Control Module References for replacement, setup, and programming.
- Ignition Coil Replacement
- Spark Plug Replacement Verification Tests