For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: A steady pulsation or 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 |

• | Refer to Powertrain On Board Diagnostic (OBD) System Check .

• | Refer to Symptoms .

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 Engine Cranks but Does Not Run .
6. If there is spark, check the spark plugs for any of the following conditions:

- | Wet plugs

- | A terminal screw that is bent or loose

- | A ceramic insulator that has cracks, carbon tracking or deposits

- | A tip insulator that has cracks, carbon tracking, deposits, or is loose

- | A center electrode that is loose

- | An incorrect spark plug gap that is too large or too small

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.

• | 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 any of the following engine mechanical problems:

- | An incorrect valve lash

- | Any broken or weak valve springs

- | An incorrect valve timing

- | An incorrect or worn camshaft

• | Check the intake and exhaust manifold passages for casting flash.

Fuel System Checks |

• | Check for a restriction in the fuel supply system. Check for the correct fuel pressure. Refer to Fuel System Diagnosis .

• | Check the fuel injectors. Perform the Fuel Injector Coil Test Procedure and the Fuel Injector Balance Test Procedure. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test .

• | Check for water contamination of the fuel.

Additional Checks |

• | Veriify that the PCM grounds are clean, tight, and in the proper locations. Refer to

#### Power and Ground

Engine Controls Components
MIL and DLC
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
G100, G101 and G102
H/L, HTR, IG and LAMP Fuses
HAZ, D/L, TAIL, STOP and DOME Fuses
BATT, ABS, FI and ACC Fuses
.

• | Check the Service Bulletins for any updates or information.