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
|
- Perform a bulletin search.
- 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
|
- 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. |
- 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
|
- Remove spark plugs and check for wet plugs, cracks, wear, improper
gap, burned electrodes, or heavy deposits. Refer to Spark Plug Visual Diagnosis.
Notice: Determine the cause of the oil or gas fouled spark plugs in order to
avoid damage to the new spark plugs.
- If a problem is found, repair as necessary.
Was a problem found?
| --
|
Go to Step 12
|
Go to Step 6
|
6
|
- 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 faulty.
|
- 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
|
- 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. |
- If a problem is found, repair as necessary. Refer to Wiring Repair
in Electrical Diagnosis
Was a problem found?
| --
|
Go to Step 12
|
Go to Step 8
|
8
|
- Check fuel pressure. Refer to
Fuel System Pressure Test
.
- If a problem is found, repair as necessary.
Was a problem found?
| --
|
Go to Step 12
|
Go to Step 9
|
9
|
- Check engine mechanical for the following conditions:
| • | Low compression. Refer to Engine Compression Test. |
| • | Sticking or leaking valves. Refer to Valve Train Diagnosis. |
| • | Worn camshaft lobe(s). Refer to Valve Train Diagnosis. |
- If a problem is found, repair as necessary.
Was a problem found?
| --
|
Go to Step 12
|
Go to Step 10
|
10
|
- Check the intake and exhaust manifold(s) for casting flash.
- If a problem is found, repair as necessary.
Was a problem found?
| --
|
Go to Step 12
|
Go to Step 11
|
11
|
- Review all diagnostic procedures within this table.
- If all procedures have been completed and no malfunctions have
been found, review/inspect the following:
| • | Visual/physical inspection. Go to Visual/Physical Checks
. |
| • | Freeze Frame data/Failure Records data. |
| • | All electrical connections within a suspected circuit and/or system.
Refer to Troubleshooting Procedures in Electrical Diagnosis. |
- 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 noted.
Is symptom still present?
| --
|
Go to Step 3
| System OK
|
