| DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as 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 low speed. |
| Preliminary |
|
| Fuel System |
|
| Sensor/System |
Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. |
| Ignition System |
- Soak the secondary ignition system with water from a spray bottle. Soaking 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 the J 26792
Spark Tester. See Special Tools
.
- Remove the spark plugs and inspect for the following:
- Correct heat range
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
Refer to Spark Plug Inspection
.
- An improper spark plug gap will cause a driveability problem. Refer to Spark Plug Inspection
. Gap the spark plugs using a wire gage gap tool. Refer to Spark Plug Replacement
.
- Determine the cause of the fouling before replacing the spark plugs.
- Visually and physically inspect the secondary ignition for the following:
- The ignition wires arcing to ground
- The ignition wires for proper engagement to spark plug
- The ignition coils for cracks or carbon tracking
- Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300
.
|
| Engine Mechanical |
- Inspect engine mechanical for the following:
- Inspect compression - Refer to Engine Compression Test
in Engine Mechanical.
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn rocker arms
- Broken valve springs
- Excessive oil in combustion chamber-Leaking valve seals. Refer to Oil Consumption Diagnosis
in Engine Mechanical.
- For incorrect basic engine parts inspect the following:
- Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearings Cleaning and Inspection
in Engine Mechanical. This could result in any of the following conditions:
- A no start
- A start and stall
- Erratic performance
Refer to Symptoms - Engine Mechanical
in Engine Mechanical for diagnostic procedures. |
| Additional Inspections |
- Inspect the exhaust system for possible restrictions. Inspect for the following:
- Inspect the exhaust system for damaged or collapsed pipes.
- Inspect the mufflers for heat distress or possible internal failure.
- Inspect for possible plugged catalytic converters. Refer to Restricted Exhaust
in Engine Exhaust.
- Electromagnetic interference (EMI) on the reference circuit can cause an engine misfire condition. A sudden increase in indicated RPM with little change in actual engine RPM change indicates EMI is present. Inspect for high voltage components near ignition control circuits if a condition exists.
- Inspect the intake manifold and the exhaust manifold passages for casting flash.
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