Cuts Out, Misses
Checks
| Action
|
DEFINITION: Steady pulsation or
jerking that follows engine speed, usually more pronounced as engine load
increases.
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Preliminary
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• | Search for service bulletins. |
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Fuel System
|
• | Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis
Testing. |
• | Check the fuel filter for being plugged or restricted. |
• | Check items which can cause an engine to run rich (long term fuel
trim significantly in the negative range). Refer to Diagnostic Aids for
DTC P0172 Fuel Trim System Rich
. |
• | Check items that can cause an engine to run lean (long term fuel
trim significantly in the positive range). Refer to Diagnostic Aids for
DTC P0171 Fuel Trim System Lean
. |
• | Check for fuel in the fuel pressure regulator vacuum hose. |
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Sensor/System
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• | Check the Oxygen sensor (O2S 1). The O2S 1 should respond quickly
to different throttle positions. If not, check the O2S 1 for silicon or other
contaminants from fuel or the use of improper RTV sealant. The sensors
may have a white powdery coating. Silicon contamination causes a
high but false O2S 1 signal voltage (rich exhaust indication). The
PCM will reduce the amount of fuel delivered to the engine, causing
a severe driveability problem. Refer to Oxygen sensor in
Information Sensors/Switches Description |
• | Check for proper operation of the MAP sensor. |
• | Check for proper operation of the TP sensor. |
• | Check for proper operation of the ECT sensor. |
|
Ignition System
|
• | Check for proper ignition voltage output with the J 26792
spark tester or equivalent. |
• | Check the spark plugs for the following conditions: |
- | Check for wet or fuel fouled spark plugs. |
- | Check for cracks on the spark plugs. |
- | Check for improper spark plug gap. |
- | Check for burned electrodes or heavy deposits. |
• | If the spark plugs are fuel or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
• | Check the Ignition Control Module (ICM) for proper ground connection. |
• | Check the ignition coils for cracks or carbon tracking. |
• | Check the spark plug wires for proper resistance and condition. |
|
Engine Mechanical
|
• | 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: |
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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. |
• | 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 for intake and exhaust manifold passages for casting flash. |
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