Checks
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DEFINITION: A steady pulsation or jerking that follows
engine speed, which is usually more pronounced as the engine load
increases. This condition is not normally felt above 1500 RPM
or 48 km/h (30 mph). The exhaust has a steady spitting
sound at idle or at low speed.
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Preliminary
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• | Refer to Important Preliminary Inspections Before Starting in
Symptoms
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Fuel System
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Sensor/System
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- Use a scan tool in order to monitor the KS system for excessive
spark retard activity. Refer to
Knock Sensor (KS) System Description
.
- An Extended Travel Brake Switch that is mis-adjusted or an Extended
Travel Brake circuit that is open causes a perceived misfire under heavy load
conditions from a stop. Use a scan tool in order to monitor the Extended
Travel Brake Switch parameter. If the scan tool displays Extended Travel
Brake Switch applied when the brake pedal is released refer to
DTC P1575 Extended Travel Brake Switch Circuit
.
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Ignition System
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• | Wet down the secondary ignition system with water from a spray
bottle. Wetting down the secondary ignition system may help locate damaged
or deteriorated components. Look/listen for arcing or misfiring
as you apply water. |
• | Test for proper ignition voltage output with spark tester J 26792
. |
• | Remove the spark plugs and inspect for the following conditions: |
• | To properly inspect the spark plugs or to correct a problem, refer
to the following procedure in Engine Electrical: |
• | An improper spark plug gap will cause a driveability concern.
Gap the spark plugs using a wire gauge gap tool. Refer to
Spark Plug Replacement
in Engine Electrical. |
• | Visually/physically inspect the secondary ignition for the following: |
- | Ignition wires arcing to ground |
- | Ignition wires for proper routing |
- | Ignition coils for cracks or carbon tracking |
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Engine Mechanical
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• | Inspect engine mechanical for the following: |
- | Sticking or leaking valves |
- | Excessive oil in combustion chamber-Leaking valve seals |
• | For more information, refer to one or more of the following procedures
in Engine Mechanical-5.7L: |
• | For incorrect basic engine parts, inspect the following components: |
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Additional Checks
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• | Inspect the following exhaust system components for possible restrictions: |
- | The exhaust system for physical damage |
- | 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 pipes
by comparing the exhaust system back pressure on each side of engine |
• | For more information, refer to the following procedures in Engine
Exhaust: |
• | Electromagnetic interference (EMI) on the reference circuit can
cause an engine miss condition. A sudden increase in RPM with little change
in actual engine RPM change indicates that EMI is present. Inspect
for high voltage components near the ignition control circuits
if a condition exists. |
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