Cuts Out, Misses Symptom
Checks
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DEFINITION: A steady pulsation or jerking that follows engine speed, usually more pronounced as the engine load increases. The exhaust has a steady spitting sound at idle, low speed or on hard acceleration.
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Preliminary Checks
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Sensor Checks
| Check the engine coolant temperature (ECT) sensor using a scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5°C (9°F) more or less than
the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or in the sensor. Refer to
Temperature Versus Resistance - Engine Coolant Temperature Sensor
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Fuel System Checks
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• | Perform the engine cylinder balance test: |
3. | Observe the engine speed for each cylinder while testing. |
4. | If there is an equal RPM drop on all cylinders, equal to within 50 RPM, the output from each cylinder is satisfactory. |
• | Check for water contamination of the fuel. |
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Ignition System Checks
| Test the ignition system for the correct operation. Verify that each coil has good crisp, blue spark. Diagnose and repair any coil with a weak spark output. Refer to
Electronic Ignition (EI) System Diagnosis
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Engine Mechanical Checks
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• | Check for any of the following engine mechanical problems: |
- | Any faulty hydraulic lifter assemblies |
- | Any broken or weak valve springs |
- | An incorrect valve timing |
- | An incorrect or worn camshaft |
• | Check the intake and exhaust manifold passages for casting flash. |
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Additional Checks
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• | An engine miss condition can be caused by electromagnetic interference (EMI) on the reference circuit. EMI can usually be detected by monitoring the engine speed with a scan tool. A sudden increase in speed with little change in the actual engine
speed change indicates EMI is present. |
• | Verify the powertrain control module (PCM) grounds are clean, tight, and in the correct locations. Refer to
Engine Controls Schematics
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