Vibration Analysis - Engine
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Vibration Analysis - Engine
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Special Tools
GE 38792-A (J-38792 )
Electronic Vibration Analyzer
The numbers below refer to the step numbers on the diagnostic table.
2
If powertrain related DTCs are present, there may be a powertrain performance condition present which could be a contributing cause to the customer's concern.
5
Making comparisons of the customer's vehicle with an equally equipped, same model year and type, KNOWN GOOD vehicle will help determine if certain disturbances may be characteristic of a vehicle design.
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Step
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Action
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Yes
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No
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Refer to
Work Stall Test Warning
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1
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Has the Vibration Analysis - Road Testing table been completed?
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Go to
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Go to
Vibration Analysis - Road Testing
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Using a scan tool, determine if any DTCs are set.
Were any DTCs set?
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Go to
Vibration Diagnosis, Starting Point, and Correction
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Go to
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3
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1.
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Block the front wheels.
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2.
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Apply BOTH the service brakes and the park brake.
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3.
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With the scan tool and an electronic vibration analyzer, if available, still installed, start the engine.
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4.
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Place the transmission in NEUTRAL or PARK.
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5.
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Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
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6.
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Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the vibration analyzer, if available.
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7.
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Place the transmission in DRIVE.
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8.
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Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
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9.
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Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the vibration analyzer, if available.
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10.
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If no frequency data was obtained, or if the vibration analyzer is not available, place the transmission into REVERSE, then repeat steps 8 and 9. Reverse-loading of the powertrain may increase or change the characteristics of the vibration.
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Were you able to duplicate the customer's concern?
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Go to
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Go to
Vibration Diagnostic Aids
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4
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Did the vibration analyzer detect a dominant frequency, or was a significant vibration present?
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Go to
Vibration Analysis - Engine/Accessory Isolation
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Go to
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Compare the test results of the customer's vehicle to the results of the same tests run, at the same engine RPM, on an equally-equipped, same model year and type, KNOWN GOOD vehicle. Refer to
Vehicle-to-Vehicle Diagnostic Comparison
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1.
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Install a scan tool into the known good vehicle.
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2.
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Install a vibration analyzer, if applicable, in the car that is in good condition. Place the sensor in the same location as in the customer's car.
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3.
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Block the front wheels.
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4.
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Apply BOTH the service brakes and the park brake.
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6.
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Place the transmission in NEUTRAL or PARK.
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7.
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Slowly increase the engine RPM to the level at which the disturbance was most noticeable in the customer's vehicle.
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8.
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Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the vibration analyzer, if available.
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9.
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Place the transmission in DRIVE.
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10.
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Slowly increase the engine RPM to the level at which the disturbance was most noticeable in the customer's vehicle.
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11.
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Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the vibration analyzer, if available.
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12.
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If no frequency data was obtained, or if a vibration analyzer is not available, place the transmission into REVERSE, then repeat steps 10 and 11. Reverse-loading of the powertrain may increase or change the characteristics of the vibration.
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Did both of the vehicles exhibit the same characteristics?
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Go to
Vibration Diagnostic Aids
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Go to
Vibration Analysis - Engine/Accessory Isolation
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