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Vibration Analysis - Engine

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. 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.

    2.

  2. 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.

Step

Action

Yes

No

Warning: Refer to Work Stall Test Warning in the Preface section.

 

1

Using a scan tool, determine if any DTCs are set.

Were any DTCs set?

Go to Diagnostic Starting Point - Vehicle

Go to Step 2

2
  1. Block the front wheels.
  2. Apply BOTH the service brakes and the handbrake.
  3. Install a scan tool.
  4. Install a vibration analyser, if available.
  5. Start the engine.
  6. Place the transmission in NEUTRAL or PARK.
  7. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  8. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on a vibration analyser.
  9. Place the transmission in DRIVE.
  10. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  11. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on a vibration analyser.
  12. If no frequency data was obtained, or if a 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.

Were you able to duplicate the customer's concern?

Go to Step 3

Go to Vibration Diagnostic Aids - Vibration Intermittent or Not Duplicated

3

Did a vibration analyser, detect a dominant frequency, or was a significant vibration present?

Go to Vibration Analysis - Engine/Accessory Isolation

Go to Step 4

4

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.

  1. Install a scan tool into the known good vehicle.
  2. Install a vibration analyzer, if available, into the known good vehicle; place the sensor in exactly the same location as it was placed in the customer's vehicle.
  3. Block the front wheels.
  4. Apply BOTH the service brakes and the handbrake.
  5. Start the engine.
  6. Place the transmission in NEUTRAL or PARK.
  7. Slowly increase the engine RPM to the level at which the disturbance was most noticeable in the customer's vehicle.
  8. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on a vibration analyser.
  9. Place the transmission in DRIVE.
  10. Slowly increase the engine RPM to the level at which the disturbance was most noticeable in the customer's vehicle.
  11. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on a vibration analyser.
  12. If no frequency data was obtained, or if a vibration analyser, 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.

Did both of the vehicles exhibit the same characteristics?

Go to Vibration Diagnostic Aids - Vibration Intermittent or Not Duplicated

Go to Vibration Analysis - Engine/Accessory Isolation

   


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