For 1990-2009 cars

#### Backfire

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 the Powertrain On Board Diagnostic (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 Checks
4 |

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

• | Clip the spark tester to engine ground.

• | Connect one end of a spark plug wire to the spark tester; connect the other end of the spark plug wire to the coil being tested.

• | Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.

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

• | Repeat the above steps for each coil.

2. If adequate spark is not present at all coils, replace coil(s) as necessary. Refer to Ignition Control Module Replacement .

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.
2. If a problem is found, repair as necessary. Refer to On-Vehicle Service in Ignition System.

Was a problem found?

--

Go to Step 12

Go to Step 6

6 |

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.

Important:: Spraying the secondary ignition wires and coils with a light mist of water may help locate an intermittent problem. Ignition components will arc to ground when a secondary component is malfunctioning.

2. If a problem is found, repair as necessary. Refer to On-Vehicle Service in Ignition System .

Was a problem found?

--

Go to Step 12

Go to Step 7

7 |

1. Refer to Troubleshooting Procedures in Electrical Diagnosis to check for an intermittent ignition system malfunction:

• | Intermittent CKP Sync signal or CKP 18X signal.

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

• | Intermittent 3X reference signal.

• | Intermittent 18X reference signal.

• | Intermittent camshaft position sensor signal.

2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis

Was a problem found?

--

Go to Step 12

Go to Step 8

8 |

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

Was a problem found?

--

Go to Step 12

Go to Step 9

9 |

1. Refer to Engine Misfire Mechanical Diagnosis in Engine General Information to check for the following conditions:

• | Low compression.

• | Sticking or leaking valves.

• | Worn camshaft lobe(s).

• | Incorrect valve timing.

• | Bent push rods.

• | Worn rocker arms.

• | Broken valve springs.

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

Was a problem found?

--

Go to Step 12

Go to Step 10

10 |

1. Check the intake and exhaust manifold(s) for casting flash.
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. Refer to Visual/Physical Checks .

• | Scan tool data. Refer to Engine Scan Tool Data List .

• | Freeze Frame data/Failure Records data.

• | All electrical connections within a suspected circuit and/or system. Refer to Troubleshooting Procedures in Electrical Diagnosis.

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

Was a problem found?

--

Go to Step 12

Review technical bulletins

12 | Operate the vehicle to duplicate conditions present when the original symptom was noticed. Is the symptom still present? | -- | Go to Step 3 | System OK