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
|
• | 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
|
• | 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 tool 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
|
• | 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
|
• | Check engine mechanical for the following: |
- | 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
Checks
|
• | 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 three-way catalytic converters for possible plugged conditions--Compare
the exhaust system back pressure on each side of engine. Check back
pressure by removing 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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