Checks
| Action
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DEFINITION: Engine
runs unevenly at idle. If severe, the engine or vehicle may shake. Engine
idle speed may vary in RPM. Either condition
may be severe enough to stall the engine.
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Preliminary Checks
|
• | Inspect the engine control module (ECM) grounds for being clean,
tight, and in the proper locations. |
• | Remove and inspect the air filter element for dirt or for being
restricted. Replace as necessary. |
|
Fuel System
|
• | Inspect for a leak in the fuel supply system. |
• | Inspect the fuel injectors. |
• | Inspect for a restricted fuel filter. |
• | Inspect for a restriction in the fuel return system. |
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Sensor/System
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• | Inspect for proper crankcase ventilation. |
• | Inspect for an intermittent crankshaft position (CKP) sensor signal
by monitoring the RPM with a scan tool. |
• | Use a scan tool in order to monitor the sensor system for unusual
sensor readings. Refer to
Scan Tool Data List
. |
|
Engine
Mechanical
|
• | Inspect engine mechanical for the following: |
- | Poor cylinder compression--2157 kPa (313 psi). |
- | Sticking or leaking valves |
- | Excessive oil in combustion chamber--Leaking valve seals. |
• | Inspect the following components for incorrect basic engine parts: |
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Additional Checks
|
• | Inspect the following components of the exhaust system for possible
restrictions: |
- | The exhaust system for damaged or collapsed pipes |
- | The exhaust manifold for a collapsed inner wall |
- | The mufflers for heat distress or possible internal failure |
• | Electromagnetic interference (EMI) on the reference circuit can
cause an engine miss condition. A scan tool can usually detect EMI by monitoring
the engine RPM. A sudden increase in RPM with
little change in actual engine RPM change indicates
that EMI is present. If a problem exists, check
routing of high voltage components, such as fuel injector
wiring, near the sensor circuits. |
• | Inspect the park neutral position (PNP) switch circuit. |
• | Inspect for faulty motor mounts. |
• | Inspect the intake manifold and the exhaust manifold passages
for casting flash. |
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