Electronic Ignition (EI) System Diagnosis
Electronic Ignition System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions 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. A voltage drop test on the circuit 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.
Reference Information
Schematic Reference
Engine Controls Schematics (LEA) Electrical Diagrams
Connector End View Reference
Component Connector End Views Outside Rearview Mirror - Driver
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References 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 [1][2]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 A 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 B 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 voltage 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 voltage circuit terminal D and ground.
• If the test lamp does not illuminate, test the ignition voltage 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 J 26792 - HEI spark tester 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