Checks
| Action
|
DEFINITION: Steady pulsation or jerking that follows engine
speed, usually more pronounced as engine load increases.
|
Preliminary
|
• | Refer to
Symptoms
, Important
Preliminary Checks Before Starting. |
• | Verify that the PCM grounds are clean, tight, and in the correct
locations. |
• | Inspect the air filter element for dirt and restrictions. Replace
the element as necessary. |
|
Fuel System
|
• | Perform the fuel injector balance test. |
• | Check for a restricted fuel filter. |
• | Check items that can cause an engine to run rich. |
• | Check items that can cause an engine to run lean. |
|
Sensor and System
|
• | Using a scan tool, monitor the knock sensor (KS) system for any
excessive spark retard activity. |
• | Check the EGR system for the correct operation. |
|
Ignition System
|
• | Remove the spark plugs and check for the following: |
• | An improper spark plug gap will cause a driveability problem.
The spark plug gapping should be done with a wire gauge gap tool. If the
spark plugs are gas or oil fouled, the cause of the fouling must be
determined before replacing the spark plugs. |
• | Check the plugs and the coils for signs of arcing, cracks, or
carbon tracking. |
• | Check for any loose ignition control module grounds. |
• | Check the spark plugs for the correct heat range. |
|
Engine Mechanical
| Check for the following conditions:
• | Any sticking or leaking valves |
• | Any worn camshaft lobes |
• | An incorrect valve timing |
• | Any broken valve springs |
• | Any excessive oil in combustion chambers or leaking valve seals |
• | A low cylinder compression |
• | Any incorrect basic engine parts. Inspect the following: |
Refer to
Base Engine Misfire Diagnosis
in Engine Mechanical.
|
Additional Checks
|
• | Check for any improper harness routing. An engine miss condition
can be caused by electromagnetic interference (EMI) on some engine controls
circuits. Use the scan tool to check for any erratic sensor values or
excessive changes in the indicated RPM with little change in the actual
engine RPM. This may indicate EMI is present. If a problem exists, check
for any improper routing of the harnesses near high voltage components
or high current components. |
• | Check the charging system. A bad diode in the alternator can allow
A/C noise to enter the electrical system. This may affect the engine controls
system operation. Refer to
Diagnostic Starting Point
in Engine Electrical. |
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