For 1990-2009 cars

#### Backfire

Checks | Actions
--- | ---
DEFINITION: The fuel ignites in the intake manifold, or the fuel ignites in the exhaust system, causing a loud popping noise.
Preliminary Checks |

• | Refer to Diagnostic System Check - Engine Controls .

• | Refer to Symptoms - Engine Controls .

• | Search the service bulletins.

Fuel System |

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

• | Check the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .

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

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

Ignition System |

• | Check for proper ignition voltage output with the J 36012-A Ignition System Diagnostic Harness and J 26792 Spark Tester or equivalent.

• | Check the spark plugs for the following conditions:

- | Wet spark plugs

- | Fuel-fouled spark plugs

- | Cracked spark plugs

- | Worn spark plugs

- | Improper spark plug gap

- | Burned electrodes

- | Heavy deposits

• | If the spark plugs are fuel or oil-fouled, determine the cause of the fouling before you replace 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 for the following conditions:

• | The compression

• | Sticking valves

• | Leaking valves

• | Worn camshaft lobes

• | Improper valve timing

• | Broken valve springs

• | Excessive oil in combustion chamber, caused by leaking valve seals

• | Low cylinder compression

• | Incorrect basic engine parts--Inspect the following:

- | The camshafts

- | The cylinder head

- | The pistons

Refer to Symptoms - Engine Mechanical in Engine Mechanical 2.2 L (L61).

Additional Checks |

• | Check intake and exhaust manifolds for casting flash.

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

- | Damaged or collapsed exhaust system pipes

- | Heat distressed or internally-failed mufflers

- | A plugged 3-way catalytic converter--Refer to Restricted Exhaust in Engine Exhaust.