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
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• | Check the engine coolant temperature (ECT) sensor using a scan tool 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. |
• | Inspect the mass air flow (MAF) sensor operation. Run the engine to normal
operating temperature. Turn OFF all accessories and observe the MAF sensor at idle
with a scan tool. If the MAF sensor reading is more than 3.5 g/s refer to
DTC P0101. |
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Fuel System Checks
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• | Check for water contamination of the fuel. |
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Ignition System Checks
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• | Check for an ignition system misfire: |
| Important: Do not perform this test for more than 2 minutes in order to prevent
damage to the catalytic converter.
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2. | Remove one ignition coil at a time using insulated pliers. |
4. | Check for spark on the suspected cylinders with a
J 26792 Spark Tester or equivalent if there is no RPM drop on one
or more cylinders. |
6. | If there is spark, inspect the spark plugs for correct operation and good
ignition system performance. Refer to
Spark Plug Inspection. |
• | Check the ignition system for moisture, dust, cracks, burns, etc. |
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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
RPM with a scan tool. A sudden increase in RPM with little change in the actual engine
RPM change indicates EMI is present. If a problem exists, check the routing of the
secondary ignition wires and the high voltage components. |
• | Verify the powertrain control module (PCM) grounds are clean, tight, and
in the proper locations. Refer to
Engine Controls Schematics. |
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