Circuit/System Testing

IMPORTANT: You must perform the Circuit/System Verification first.

Verify that the following conditions do not exist:
- The fuel injector wire harness electrical connectors are connected to the wrong fuel injectors. Refer to Engine Controls Schematics .
- Engine vacuum leaks
- Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis (w/o FPCM) or Fuel System Diagnosis (FPCM) .
- Contaminated fuel-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool) .
- Restricted exhaust system-Refer to Restricted Exhaust .
- If you find any of the above conditions, repair as necessary.
Verify that there is no misfire on cylinders 1, 4, 6, or 7 due to cylinder deactivation-Refer to Cylinder Deactivation (Active Fuel Management) System Diagnosis .
Ignition OFF, install the J 26792: Tester to the spark plug wire boot of the misfiring cylinder.

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

Attempt to start the engine and observe the J 26792: Tester. The spark tester should spark.
- If there is no spark, test the spark plug wire for the correct resistance, refer to Ignition System Specifications and Spark Plug Wire Inspection .
- If the spark plug wire tests normal, refer to Electronic Ignition 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, or incorrectly gapped-Refer to Spark Plug Inspection .
- 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.
Operate the engine under the conditions in which the misfire occurred. This may include putting the engine under a load or allowing the engine to return to a cold condition. Observe the Misfire Current Counters with a scan tool. The misfire should not follow the spark plug exchange.
- If the misfire follows with 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 (CH47976) or Fuel Injector Diagnosis (J39021 or Scan Tool) .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical .