For 1990-2009 cars

#### Backfire Symptom

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Definition: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.
1 | Did you perform the On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is present, correct the condition as instructed in the bulletin.

Did you find a bulletin that addresses the symptom?

--

Go to Step 12

Go to Step 3

3 | Did you perform a visual/physical check? | -- | Go to Step 4 | Go to Symptoms
4 |

1. Check for a proper ignition coil output voltage with spark tester J 26792 (ST 125):

• | Clip the spark tester J 26792 to engine ground.

• | Connect one end of a spark plug wire to the spark tester J 26792 . Leave the other end of the spark plug wire connected to the coil being tested.

• | Disconnect the spark plug wire from the other spark plug on the same coil being tested, and ground the wire.

• | Crank the engine while observing the spark tester J 26792 . Look for a blue spark.

• | Repeat the above steps for each coil.

2. If an adequate spark is not present at all of the coils, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 5

5 |

1. Remove the spark plugs. Check for the spark plugs for the following conditions:

• | Wet plugs

• | Cracks

• | Excessive wear

• | An improper gap

• | Burned electrodes

• | Carbon tracking on the insulator

• | Heavy deposits. Refer to Ignition System Check

Notice: Determine the cause of the oil or gas fouled spark plugs in order to avoid damage to the new spark plugs.

2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 6

6 |

Important: Spray the secondary ignition wires with a light mist of water in order to help locate an intermittent problem. The ignition components will arc to ground when a secondary component is malfunctioning. Refer to Ignition System Check

1. Visually/Physically inspect the secondary ignition components. Check the components for the following conditions:

• | Check the ignition wires for cross firing.

• | Check the ignition wires arcing to ground.

• | Check the ignition wires for improper routing.

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

2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 7

7 |

1. Check for an intermittent ignition system malfunction:

• | Check the primary connections at the ignition coil assembly.

• | Check for any intermittent connections at the Crankshaft Position sensor.

2. If a problem is present, repair as necessary. Refer to Engine Electrical, and Troubleshooting Procedures for the proper procedure. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis .

Was a problem found?

--

Go to Step 12

Go to Step 8

8 |

1. Check the fuel pressure. Refer to Fuel System Diagnosis .
2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 9

9 |

1. Check for the following Engine Mechanical problems (Refer to Engine Mechanical ):

• | Low compression

• | Sticking valves

• | A hydraulic valve lifter problem

• | Leaking cylinder head gaskets

• | A worn or incorrect camshaft

• | Incorrect cam timing

• | A damaged timing belt

2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 10

10 |

1. Check the intake and the exhaust manifold(s) for casting flash. Refer to Engine Mechanical.
2. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 11

11 |

1. Review all of the diagnostic procedures within this table.
2. If all of the procedures have been completed and no malfunctions have been found, review/inspect the following:

• | The scan tool data

• | The Freeze Frame data

• | All of the electrical connections within a suspected circuit and/or system

3. If a problem is present, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 3

12 | Operate the vehicle under the same conditions (as closely as possible) as when the original symptom occurred. Is the original symptom still present? | -- | Go to Step 3 | Repair complete. If another driveability symptom exists, refer to Symptoms .