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

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

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Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

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?

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Go to Step 12

Go to Step 3

Was visual/physical check performed?

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Go to Step 4

Go to Visual/Physical Checks

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.

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

Was a problem found?

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Go to Step 12

Go to Step 5

1. 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.

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

Was a problem found?

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Go to Step 12

Go to Step 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 faulty.

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

Was a problem found?

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Go to Step 12

Go to Step 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.

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

Was a problem found?

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Go to Step 12

Go to Step 8

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

Was a problem found?

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Go to Step 12

Go to Step 9

1. 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.

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

Was a problem found?

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Go to Step 12

Go to Step 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?

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Go to Step 12

Go to Step 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. Go to Visual/Physical Checks .

•	Scan tool data. Go 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?

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Go to Step 12

Review technical bulletins

Operate the vehicle to duplicate conditions present when the original symptom was noted.

Is symptom still present?

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Go to Step 3

System OK