Circuit/System Testing

Verify that the following conditions do not exist:
- The fuel injector wire harness electrical connectors are connected to the proper fuel injectors. Refer to Engine Controls Schematics .
- Engine 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 .
- Restricted exhaust system-Refer to Restricted Exhaust .
- If you find any of the above conditions, repair as necessary.
Ignition OFF, remove the spark plug wire from the spark plug and ignition coil. Inspect and test the spark plug wire for arching, cuts, rubbing on other components, and proper resistance. Refer to Spark Plug Wire Inspection and Ignition System Specifications .
- If a fault is found, replace the spark plug wire. Refer to Spark Plug Wire Replacement .
Install the spark plug wire to the ignition coil.
Install the J 26792 to the boot of the spark plug wire and ground. See Special Tools .

IMPORTANT: 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 for diagnosis of the ignition coil.
Ignition OFF, remove the spark plug from the misfiring cylinder. Verify that the following conditions do not exist with the spark plug:
- Gas, coolant, or oil fouled
- Cracked, worn, incorrectly gapped-Refer to Spark Plug Inspection .
- If there is a condition with the spark plug, replace the spark plug.
Exchange the spark plug with another cylinder that is operating correctly.
Operate the engine under the conditions in which the misfire occurred. This may include putting the engine under a load, turning on the A/C, seat heaters, and rear window defog. Observe the Misfire Current Counters with a scan tool. 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-Refer to Fuel Injector Diagnosis (w/CH47976) or Fuel Injector Diagnosis (w/J39021 or w/Tech 2) .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical .