Circuit/System Testing

Verify 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 .
- Restricted exhaust system - Refer to Restricted Exhaust .
- If you find any of the above conditions, repair as necessary.
Ignition OFF, remove the ignition coil of the misfiring cylinder.
Connect the harness connector of the removed ignition coil.
Install a J 26792 to the spark plug boot of the removed ignition coil. 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 . The spark tester should spark.
- If there is no spark, test the spark plug boot for carbon tracking, corrosion, or water contamination. If the spark plug boot tests normal, refer to Electronic Ignition (EI) System Diagnosis for diagnosis of the ignition system.
Ignition OFF, remove the spark plug from the misfiring cylinder. Verify the following conditions do not exist with the spark plug:
- Gas, coolant, or oil fouled - Refer to Spark Plug Inspection .
- Cracked, worn, 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 the spark plug of another cylinder that is operating correctly.
Engine running, observe the scan tool Misfire Current Counter parameter. The misfire should not follow the spark plug exchange.
- If the misfire follows the spark plug, replace the spark plug.
Disconnect the harness connector at the fuel injector of each misfiring cylinder.
Install a J 34730-2B at the harness connector of a misfiring cylinder. See Special Tools .
Engine cranking, verify the injector test lamp flashes ON and OFF.
- If the injector test lamp does not flash, refer to Fuel Injector Circuit Diagnosis .
If all tests are normal, test for the following:
- A lean or rich fuel injector - Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) .
- An engine mechanical condition - Refer to Symptoms - Engine Mechanical .