Checks
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DEFINITION: Steady
pulsation or jerking that follows engine speed, usually more pronounced as
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 low
speed.
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Preliminary
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• | Refer to
Symptoms
, Important Preliminary Checks Before Starting.
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• | Check PCM grounds for being clean, tight and in their proper locations.
Refer to PCM wiring diagrams in Electrical Diagnosis.
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Fuel System
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Sensor/System
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• | Using a scan tool, monitor KS system for excessive spark retard
activity. |
• | Check the EGR system for proper operation. |
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Ignition System
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• | Wetting down the secondary ignition system with water from a spray
bottle may help locate damaged or deteriorated components. Look/listen for
arcing or misfiring as water is applied. |
• | Check for proper ignition voltage output with spark tester J 26792.
Refer to Distributor Ignition System for procedure. |
• | Remove spark plugs and check for the following: |
• | An improper spark plug gap will cause a driveability problem.
Refer to spark plug gap specification is Section OB. The spark plug gapping
should be done using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement.
If spark plugs are gas or oil
fouled, the cause of the fouling must be determined before replacing the
spark plugs. Refer to
DTC P0172 Fuel Trim System Rich Bank 1
and
DTC P0175 Fuel Trim System Rich Bank 2
to determine the Rich condition or Engine Mechanical
for the oil fouling condition. |
• | Visually/Physically inspect Secondary ignition for the following: |
- | Ignition wires for cross firing. |
- | Ignition wires arcing to ground. |
- | Ignition wires for proper routing. |
- | Distributor cap for cracks or carbon tracking. |
• | Wetting down the secondary ignition system with water from a
spray bottle may help locate damaged or deteriorated components. Look/listen
for arcing or misfiring as water is applied. |
• | Spark plugs for proper heat range. Refer to Owners Manual or Section OB.
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Engine Mechanical
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• | Check engine mechanical for the following: |
- | Sticking or leaking valves. |
- | Excessive oil in combustion chamber-Leaking valve seals. |
- | Low cylinder compression. |
• | For incorrect basic engine parts. Inspect the following: |
Refer to Engine Mechanical
for diagnosis
procedures.
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Additional Checks
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• | Check exhaust system for possible restrictions. Check for the
following: |
- | Inspect exhaust system for damaged or collapsed pipes. |
- | Inspect mufflers for heat distress or possible internal failure. |
- | For possible plugged Three-Way catalytic converters by
comparing exhaust system back pressure on each side of engine. Check back
pressure by removing AIR check valves near exhaust manifolds. Refer to Restricted
Exhaust System Check and Exhaust System. |
• | An engine miss condition can be caused by Electromagnetic Interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM with little change
in actual engine RPM change, indicates EMI is present. If a problem exists,
check routing of secondary ignition wires, high voltage components (Near
Ignition Control circuits). Check distributor ground circuit for being open
or loose. |
• | Check for intake and exhaust manifold passages for casting flash.
Refer to Engine Mechanical.
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