Backfire

Definition: Fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.

1. Was the "On-Board Diagnostic (OBD) System Check" performed?

[YES] Go to Step 2.
[NO] Go to OBD System Check. Description of On-Board Diagnostics

2. a. Perform a bulletin search.
b. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.
c. Was a bulletin found that addresses the symptom?

[YES] Verify repair.
[NO] Go to Step 3.

3. Was a visual/physical check performed?

[YES] Go to Step 4.
[NO] Go to Visual/Physical Check. Visual/Physical Check

4. a. Check for proper ignition coil voltage output with spark tester J 26792 (ST-125).
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 5.

5. a. Remove the spark plugs and check for gas or oil fouling, cracks, wear, improper gap, burned electrodes of heavy deposits.

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

b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 6.

6. a. Visually/physically inspect the ignition coils for cracks.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 7.

7. a. Check for an intermittent ignition system malfunction:
- Intermittent Crankshaft Position (CKP) 58X signal.
- Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 8.

8. a. Check the fuel pressure. Refer to Fuel System Pressure Test.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 9.

9. a. Check for the following engine mechanical problems:
- Low compression.
- Worn or camshaft lobe(s).
- Incorrect valve timing.
- Sticking or leaking valves.
- Camshaft drive belt slipped or stripped.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 10.

10. a. Check the intake and exhaust manifold(s) for casting flash.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 11.

11. a. Review all diagnostic procedures within this table.
b. 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 buffer.
- All electrical connections within a suspected circuit and/or system.
c. If a problem is found, repair as necessary.
d. Was a problem found?

[YES] Verify repair.
[NO] Contact Technical Assistance.