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 the 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 the fuel injectors. Refer to Fuel Injector Balance 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 Fuel Controls.

Ignition System |

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

• | Check the spark plugs for the following conditions:

- | Check for wet or fuel fouled spark plugs.

- | Check for cracks on the spark plugs.

- | Check for wear.

- | Check for improper spark plug gap.

- | Check for 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:

- | Compression.

- | Sticking or leaking valves.

- | Worn camshaft(s) lobe(s).

- | Valve timing.

- | Broken valve springs.

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

- | Low cylinder compression.

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

- | Camshafts

- | Cylinder head

- | Pistons, etc.

• | Refer to Engine Mechanical.

Additional Checks |

• | Check Intake and exhaust manifold(s) for casting flash. Refer to 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 .