For 1990-2009 cars

#### Backfire

Tests/Inspections | Actions
--- | ---
DEFINITION: Fuel ignites in the intake manifold, or in the exhaust system, making loud popping noise.
Preliminary |

• | Refer to Diagnostic System Check - Engine Controls .

• | Refer to Symptoms - Engine Controls .

• | Search for service bulletins.

Fuel System |

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

• | Test the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2 .

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

• | Ensure that each fuel injector harness is connected to the correct injector. Refer to

#### Power, Ground, and Injectors

Master Electrical Component List
Powertrain Control Module Description
Engine Data Sensors
Power, Ground, KS, CMP, CKP Coils, and ICM
OBD II Symbol Description Notice
G103 and G105
Compressor Controls
IGN SW-BATT2, WIPER, AIR BAG, TURN LPS, IGN MOD, BU LMP, PCM IGN, F/PINJR, A/C BFC, AUTO TRANS, ABS, IGN Fuses
.

Ignition System |

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

• | Inspect the spark plugs for the following conditions:

- | Any wet or fuel fouled plugs

- | Any cracks

- | An incorrect gap

- | Any burnt electrodes or heavy deposits

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

• | Inspect the ignition control module (ICM) for a correct ground connection.

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

Engine Mechanical |

• | Inspect for the following conditions:

- | A low compression. Refer to Engine Compression Test in Engine Mechanical.

- | Any broken valve springs.

- | Any sticking or leaking valves.

- | Any worn camshafts lobes.

- | Any valve timing.

- | Any excessive oil in a combustion chamber or leaking valve seals. Refer to Oil Consumption Diagnosis in Engine Mechanical.

- | Refer to Symptoms - Engine Mechanical in Engine Mechanical.

• | Check for incorrect basic engine parts. Inspect the following:

- | The camshafts

- | The cylinder head

- | The pistons, etc.

- | Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional |

• | Inspect the intake manifold and the exhaust manifolds for casting flash. Refer to Symptoms - Engine Mechanical in Engine Mechanical .

• | Inspect the exhaust system for the following conditions:

- | Any damaged or collapsed pipes

- | Any heat distress or internal failure of the muffler

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