Circuit/System Testing

NOTE:

You must perform the Circuit/System Verification first.

Verify that the following conditions do not exist:
- The Q17 fuel injector wire harness electrical connectors are connected to the wrong Q17 fuel injectors. Refer to Engine Controls Schematics .
- Engine vacuum leaks
- Crankcase ventilation system 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, install the J-26792 spark 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 spark 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 resistance is not the specified value, replace the wire.
- If the spark plug wire tests normal, refer to Electronic Ignition System Diagnosis for diagnosis of the T8 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 Q17 fuel injector-Refer to Fuel Injector Diagnosis (CH47976) , Fuel Injector Diagnosis (J39021 or Scan Tool) .
- 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 .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical (L76, L77) .