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Vibration Analysis - Engine

Special Tools

EL-38792-A Electronic Vibration Analyzer (EVA) 2

For equivalent regional tools, refer to Special Tools and Equipment .

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

Has the Vibration Analysis - Road Testing table been completed?

Go to Step 2

Go to Vibration Analysis - Road Testing

2

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

Were any DTCs set?

—

Go to Step 3

3
  1. Block the front wheels.
  2. Apply BOTH the service brakes and the handbrake.
  3. With the scan tool and the EL-38792-A analyser (EVA) 2 , if available, still installed, start the engine.
  4. Place the transmission in NEUTRAL or PARK.
  5. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  6. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the EL-38792-A analyser (EVA) 2 , if available.
  7. Place the transmission in DRIVE.
  8. Slowly increase the engine RPM to the level at which the disturbance is most noticeable.
  9. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the EL-38792-A analyser (EVA) 2 , if available.
  10. If no frequency data was obtained, or if the EL-38792-A analyser (EVA) 2 , is not available, place the gearbox 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 4

Go to Vibration Diagnostic Aids

4

Did the EL-38792-A analyser (EVA) 2 detect a dominant frequency, or was a significant vibration present?

Go to Vibration Analysis - Engine/Accessory Isolation

Go to Step 5

5

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 .

  1. Install a scan tool into the known good vehicle.
  2. Install the EL-38792-A analyser (EVA) 2 , 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 the EL-38792-A analyser (EVA) 2 , if available.
  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 the EL-38792-A analyser (EVA) 2 , if available.
  12. If no frequency data was obtained, or if the EL-38792-A analyser (EVA) 2 , is not available, place the gearbox 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

Go to Vibration Analysis - Engine/Accessory Isolation

   


© Copyright Chevrolet. All rights reserved
   


© Copyright Chevrolet. All rights reserved