Checks
| Action
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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 1,500 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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• | Inspect the powertrain control module (PCM) grounds for being
clean, tight, and in the proper locations. Refer to
Engine Controls Schematics
. |
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Fuel System
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• | Inspect the items which can cause an engine to run rich, having
the long term fuel trim near -13 percent. For a rich condition,
refer to
DTC P0131 or P0151
and
DTC P0132 or P0152
. |
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Sensor/System
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- Use a scan tool in order to monitor the knock sensor (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
.
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Ignition System
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• | Wet the secondary ignition system with water from a spray bottle.
Wetting the secondary ignition system may help locate damaged
or deteriorated components. Look and listen for arcing or misfiring
as you apply water. |
• | Test for proper ignition voltage output with J 26792
Spark Tester. |
• | Remove the spark plugs and inspect for the following conditions: |
• | In order to properly inspect the spark plugs or to correct a condition,
refer to the following procedures: |
• | 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
. |
• | Determine the cause of the fouling before replacing the spark
plugs if the spark plugs are gas, coolant or oil fouled. Refer to
DTC P0172 or P0175
for diagnosis of the
rich condition. Refer to
Spark Plug Inspection
for diagnosis of coolant or oil fouled spark plugs. |
• | Visually and physically inspect the secondary ignition for the
following conditions: |
- | The ignition coils for cracks or carbon tracking |
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Engine Mechanical
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• | Inspect engine mechanical for the following conditions: |
- | Sticking or leaking valves |
- | Excess oil in the combustion chamber-Inspect for leaking
valve seals. |
• | For more information, refer to one or more of the following procedures
in Engine Mechanical-5.7L: |
• | Inspect for incorrect engine parts, such as the following basic
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 for possible internal failure |
- | The 3-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 the actual engine RPM change indicates that EMI is present.
Inspect for any high voltage components near the ignition
control circuits if a condition exists. |
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