| 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 |
- Verify that the engine coolant temperature (ECT) sensor is not shifted in value. Refer to Temperature vs Resistance
.
- Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity. Refer to Scan Tool Data List
.
- Inspect for throttle body tampering, excessive deposits, or damage.
- Inspect for a vacuum leak.
- Inspect the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis
in Engine Mechanical.
|
| Ignition System |
- In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures:
- Inspect for proper secondary ignition voltage output with J 26792
HEI Spark Tester. See Special Tools
.
- Inspect the distributor cap and rotor. Refer to Distributor Inspection
.
- An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool.
- If the spark plugs are found to be fouled, determine the cause before replacing the spark plugs.
- Inspect for damaged spark plug wires. Refer to Spark Plug Wire Inspection
.
- Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300
.
- 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 the water.
|
| Engine Mechanical |
- Inspect engine mechanical for the following:
- For incorrect, worn, or damaged basic engine parts, inspect the following:
- Refer to Symptoms - Engine Mechanical
in Engine Mechanical for diagnosis procedures.
- Inspect for excessive end play 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
|
| 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) can cause an engine misfire condition. A sudden increase in indicated RPM parameter 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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