Checks
| Actions
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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 Checks
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Fuel System
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• | Check that each injector harness is connected to the correct injector
or cylinder according to the firing order firing order: 1-8-7-2-6-5-4-3.
Relocate injector harnesses as necessary. |
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Sensor/System
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• | Check the secondary air injection (AIR) system. |
• | Check the air intake system and crankcase for air leaks. |
• | Check 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. |
• | Check for proper calibration of speedometer. Connect J 33431-B
Signal Generator to the vehicle speed
sensor (VSS) electrical connector. Ignition ON, tester ON and monitor the speedometer.
The speedometer should indicate 86 km/h (54 mph). |
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Ignition System
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• | Check for proper ignition voltage output with J 26792
Spark Tester . |
• | Check for an intermittent ignition system malfunction in the following
circuits: |
- | Intermittent ignition control circuit. |
- | Use the scan tools Snapshot feature in order to help locate an intermittent
ignition failure. |
• | Remove spark plugs and check for the following: |
• | An improper spark plug gap will cause a driveability problem. Gap the
spark plugs using a wire gauge gap tool. Refer to
Spark Plug Replacement
. |
• | Determine the cause of the fouling before replacing the spark plugs
if the spark plugs are gas, coolant, or oil fouled. Refer to one of the following
procedures: |
• | Visually and physically inspect the secondary ignition for the following: |
- | Ignition wires arcing to ground |
- | Ignition 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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• | Check the engine coolant level for being low. Refer to
Loss of Coolant
in Engine Cooling. |
• | Check the engine thermostat for proper operation and for the correct
heat range. Refer to
Thermostat Diagnosis
in Engine Cooling. |
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Engine Mechanical
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• | Check the engine for the following mechanical conditions: |
- | Sticking or leaking valves |
• | Inspect the following components for incorrect basic engine parts: |
• | Refer to the appropriate procedures in Engine Mechanical 8.1L for
diagnosis procedures. |
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Additional Checks
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• | Visually and physically check the vacuum hoses for splits, kinks, and
proper connections and routing as shown on the Vehicle Emission Control Information
label. |
• | Check 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 |
- | The 3-way catalytic converters for possible plugged conditions--Compare
the exhaust system back pressure on each side of engine. Check back
pressure by removing secondary air injection (AIR) check valves near exhaust
manifolds. Refer to
Restricted Exhaust
in Engine Exhaust. |
• | 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, check for high voltage components
near the ignition control circuits. |
• | Check the park/neutral position (PNP) switch operation. |
• | Check the intake manifold and the exhaust manifold passages for casting
flash. |
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