For 1990-2009 cars

#### Backfire

Checks | Actions
--- | ---
Definition: Fuel ignites in the intake manifold, or in the exhaust system, making loud popping noise.
Preliminary Checks |

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

• | Refer to Symptoms .

• | Search for service bulletins.

Fuel System |

• | Check for low fuel pressure. Refer to Fuel System Diagnosis .

• | Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Ensure each injector harness is connected to the correct injector/cylinder. Refer to Engine Controls Schematics .

Ignition System |

• | Check for proper ignition voltage output with the spark plug jumper wires J 36012-A and spark tester J 26792 .

• | Check the spark plugs for the following conditions:

- | Wet or fuel fouled spark plugs

- | Cracks on the spark plugs

- | Wear

- | Improper spark plug gap

- | Burned electrodes or heavy deposits

• | If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

• | Check the ignition control module (ICM) for proper ground connection.

• | Check the ignition coils for cracks or carbon tracking.

Engine Mechanical |

• | Check engine mechanical:

- | Check compression.

- | Sticking or leaking valves.

- | Worn camshaft lobes.

- | Valve timing.

- | Bent push rods.

- | Worn rocker arms.

- | Broken valve springs.

- | Excessive oil in combustion chamber-Leaking valve seals.

- | Low cylinder compression.

• | For incorrect basic engine parts. Inspect the following:

- | Camshaft

- | Cylinder heads

- | Pistons, etc.

• | Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional Checks |

• | Check Intake and exhaust manifolds for casting flash. Refer to Intake Manifold Replacement and to Exhaust Manifold Replacement in Engine Mechanical.

• | Check the exhaust system for possible restriction. Check the following:

- | Inspect exhaust system for damaged or collapsed pipes.

- | Inspect mufflers for heat distress or possible internal failure.

- | For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check .