Circuit/System Testing
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- 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 (Except LZ1) .
- Engine vacuum leaks
- Fuel pressure that is too low or too high-Refer to Fuel System Diagnosis (Without FPCM) , Fuel System Diagnosis (FPCM) .
- 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.
- 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 spark tester to the spark plug wire boot of the misfiring cylinder.
- 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 the specified value, replace the wire.
- 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) , Fuel Injector Diagnosis (J39021 or Scan Tool) .
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical .
NOTE:
You must perform the Circuit/System Verification first.
NOTE:
An erratic or weak spark is considered a no spark condition.