Diagnostic Instructions
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:
| • | An ignition voltage circuit |
| • | An IC control circuit |
| • | A 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. To pinpoint this condition perform a voltage drop test on the circuit.
Reference Information
Schematic Reference
Engine Controls Schematics
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Special Tools Required
J 26792
HEI Spark Tester
Circuit/System Verification
Important: Verify that the engine is in good mechanical condition before continuing with this diagnostic.
| • | Observe the Engine Controls Schematic for the ignition coils/modules, and review the Ignition System Specifications and the spark plug inspection procedure to verify the following: |
| - | The ignition coil/modules are correctly connected |
| - | The proper firing order |
| - | The proper spark plug type |
| - | The proper spark plug gap and torque |
| • | A 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. |
Circuit/System Testing
- Ignition OFF, disconnect the ignition coil/module harness connector at the affected ignition coil/modules.
- Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the ground circuit terminal 1or A and ground.
| ⇒ | If greater than the specified value, test the ground circuit for an open/high resistance. |
- Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the low reference circuit terminal 2 or B 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. |
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.
- Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 4 or D and ground.
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. |
- Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
- Start the engine, observe the scan tool Misfire Current Cylinder parameters.
| ⇒ | If the misfire transfers with the suspect ignition coil/module, replace as needed. |
| ⇒ | If the misfire does not transfer with the suspect ignition coil/module, refer to the Component Testing procedures below, and replace the spark plug if necessary. |
Component Testing
| • | Use the Spark Plug Inspection procedure to verify the integrity of the spark plugs. Refer to
Spark Plug Inspection
. |
| • | Use the
J 26792
to verify the output of each ignition coil/module. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
