Inspections
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DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
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Preliminary
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Fuel System
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• | Test that each injector harness is connected to the correct injector or cylinder. Relocate injector harnesses as necessary. |
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Sensor/System
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• | Inspect the air intake system and crankcase for air leaks. |
• | Test the crankcase ventilation valve for proper operation. Place a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve. |
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Ignition System
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• | Test for proper ignition voltage output with a
J 26792
Spark Tester. |
• | Test for an intermittent ignition system malfunction in the following circuits: |
- | Intermittent ignition control circuit. |
- | Use the scan tool Snapshot feature in order to help locate an intermittent ignition failure. |
• | An improper spark plug gap may cause a driveability problem. Gap the spark plugs using a wire gage gap tool. Refer to
Spark Plug Replacement
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• | Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant, or oil fouled. Refer to
Spark Plug Inspection
for diagnosis of fouled spark plugs. |
• | Visually and physically inspect the secondary ignition for the following: |
- | Spark plug wires arcing to ground |
- | Spark plug wires for proper routing |
• | Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. |
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Engine Cooling System
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• | Inspect the engine coolant level for being low. Refer to
Loss of Coolant
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• | Test the engine thermostat for proper operation and for the correct heat range. |
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Engine Mechanical
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• | Inspect engine mechanical for the following conditions: |
- | Sticking or leaking valves |
• | Inspect the following components for incorrect basic engine parts. Refer to the appropriate procedures in Engine Mechanical for diagnosis procedures: |
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Additional
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• | Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections and routing as shown on the Vehicle Emission Control Information label. |
• | Inspect the intake manifold and the exhaust manifold passages for casting flash. |
• | Inspect the following components of the exhaust system for possible restrictions: |
- | The exhaust system for damaged or collapsed pipes |
- | The exhaust manifold for a collapsed inner wall |
- | The mufflers for heat distress or possible internal failure |
- | Compare the exhaust system back pressure on each side of engine. Refer to
Restricted Exhaust
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• | Electromagnetic interference (EMI) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM change may indicate
that EMI is present. If a problem exists, inspect for high voltage components near the ignition control circuits. |
• | Inspect the park/neutral position (PNP) switch operation. |
• | Inspect the intake manifold and the exhaust manifold passages for casting flash. |
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