For 1990-2009 cars

#### Backfire Symptom

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Definition: Fuel ignites in the intake manifold, or in the exhaust system, making loud popping noise.
1 | Was the Powertrain On Board Diagnostic (OBD) system check performed? | -- | Go to Step 2 | Go to Powertrain OBD System Check
2 |

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

Was a bulletin found that addresses the symptom?

--

Go to Step 12

Go to Step 3

3 | Was visual/physical check performed? | -- | Go to Step 4 | Go to Visual /Physical Check
4 |

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

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

• | Connect J 26792 to an ignition wire then ground spark plug end of ignition wire from companion cylinder. The companion cylinder is the cylinder that shares the same ignition coil.

• | Crank the engine while observing the spark tester J 26792; a crisp blue spark should be observed.

• | Repeat the above steps for each coil.

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

Was a problem found?

--

Go to Step 12

Go to Step 5

5 |

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

1. Remove spark plugs and check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Refer to Electronic Ignition System
2. Refer to DTC P0172 to help find the cause of a rich condition or Engine Mechanical for an oil fouling condition.
3. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 12

Go to Step 6

6 |

Important: Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is faulty. Refer to Electronic Ignition in Engine Electrical.

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

• | Ignition wires for cross firing.

• | Ignition wires arcing to ground.

• | Ignition wires for improper routing.

• | Ignition coils for cracks or carbon tracking

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

Was a problem found?

--

Go to Step 12

Go to Step 7

7 |

1. Check for an intermittent ignition system malfunction:

• | Intermittent CKP Sync or CKP 24X signal.

• | Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position sensor.

• | Intermittent 3X reference signal.

• | Intermittent 24 X reference signal.

• | Intermittent Camshaft position signal.

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

Was a problem found?

--

Go to Step 12

Go to Step 8

8 |

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

Was a problem found?

--

Go to Step 12

Go to Step 9

9 |

1. Check engine mechanical for the following conditions. Refer to Engine Mechanical for diagnosis procedures.

• | Low compression.

• | Sticking or leaking valves.

• | Worn camshaft lobe(s).

• | Incorrect valve timing.

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

Was a problem found?

--

Go to Step 12

Go to Step 10

10 |

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

Was a problem found?

--

Go to Step 12

Go to Step 11

11 |

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

• | Visual/physical inspection.

• | Scan Tool data.

• | Freeze Frame data/Failure Records Data.

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

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

Was a problem found?

--

Go to Step 12

Review Technical Service Bulletins

12 | Operate the vehicle to duplicate conditions present when the original symptom was noted. Is symptom still present? | -- | Go to Step 3 | Repair Complete