Circuit/System Testing

Verify that the following conditions do not exist:
- Vacuum hose splits, kinks, and incorrect connections
- Engine vacuum leaks
- Crankcase ventilation system for vacuum leaks
- Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis .
- Contaminated Fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) .
- Exhaust system restrictions
- If you find any of the above conditions, repair as necessary.
Ignition OFF, remove the ignition coil of the misfiring cylinder, but leave the electrical connector connected.
Inspect the ignition coil boot for the following conditions:
- Holes
- Tears
- Carbon tracking
- Oil contamination
- water intrusion
- If you find any of the above conditions, repair as necessary.
Install the J 26792 to the boot of the appropriate ignition coil and ground. See Special Tools .

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

Attempt to start the engine and observe the J 26792 . See Special Tools . The spark tester should spark.
- If there is no spark, refer to Electronic Ignition (EI) System Diagnosis (w/LLT) for diagnosis of the ignition coil.
Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the spark plug does not exhibit the following conditions:
- Gas, coolant, or oil fouled-Refer to Spark Plug Inspection .
- Cracked, worn, incorrectly gapped-Refer to Ignition System Specifications .
- If there is a condition with the spark plug, replace the spark plug.
Exchange the suspected spark plug with another cylinder that is operating correctly.
Engine idling, observe the scan tool Misfire Current Counter parameters. The misfire should not follow the spark plug exchange.
- If the misfire follows the spark plug, replace the spark plug.
If all conditions test normal, test or inspect for the following:
- A lean or rich fuel injector.
- An engine mechanical condition-Refer to SYMPTOMS - ENGINE MECHANICAL .