DEFINITION: A repetitive jerking that follows engine speed, usually more pronounced as the engine load increases. The exhaust has a steady spitting sound at idle, low speed or on hard acceleration.

Preliminary Checks

Ignition System Checks

Check for an ignition system misfire:

Important: DO NOT perform this test for more than 2 minutes in order to prevent damage to the catalytic converter.

1. Start the engine.
2. Disconnect one fuel injector at a time while observing engine RPM.
3. An equal RPM drop on all cylinders, within 50 RPM, indicates a common condition that is affecting all cylinders.
4. No RPM drop on one or more cylinders indicates a cylinder specific condition. Check for spark on the suspected cylinders with a J 26792 spark tester or equivalent.
5. If there is no spark, refer to Electronic Ignition (EI) System Diagnosis .
6. If there is spark, check the spark plugs for damage and ware. Refer to Spark Plug Inspection .
7. Check the ignition coil spark plug boots for cracks, carbon tracking, and moisture.
8. If the ignition system components of the suspect cylinder pass all checks, inspect the cylinder for mechanical or fuel delivery faults.

•	Run the engine and spray the ignition system with water in order to check for secondary voltage shorts.

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Check the engine reference signal of the camshaft position (CMP) sensor with a scan tool. Observe the Engine Speed parameter while operating the engine at the speed of the concern. The scan tool should indicate steady and linear RPM readings while running. If the erratic values, such as sudden spikes or drops in engine speed are displayed, the engine reference signal is not stable enough for the engine to run properly. Inspect the CMP sensor signal rotor and housing for worn bushings or drive coupling. Inspect for electromagnetic interference (EMI) of the reference signal.

Engine Mechanical Checks

Check for mechanical engine problems. Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Fuel System Checks

Additional Checks