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

Were you sent here from the Vibration Analysis - Engine/Accessory Isolation table?

Go to Step 2

Go to Vibration Analysis - Engine/Accessory Isolation

2

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Remove the flywheel/flexplate-to-torque converter bolts access cover, if equipped.
3. Determine if sufficient clearance exists to separate the transmission torque converter away from the engine flywheel/flexplate and safely secure the torque converter from accidentally engaging with the flywheel/flexplate.

Is there sufficient clearance to separate and safely secure the transmission torque converter away from the engine flywheel/flexplate?

Go to Step 3

Go to Step 9

3

1. With the flywheel/flexplate-to-torque converter access cover still removed, and with the vehicle still raised, mark the position of the transmission torque converter in relation to the engine flywheel/flexplate.
2. Disconnect the torque converter and move it away from the flywheel/flexplate.
3. Secure the transmission torque converter away from the engine flywheel/flexplate.
4. Lower the vehicle, start the engine and allow the engine to idle.
5. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
6. Visually inspect the flywheel/flexplate for excessive lateral runout.
7. Lower the vehicle.
8. Turn OFF the ignition.

Did the flywheel/flexplate exhibit excessive lateral runout?

Go to Step 6

Go to Step 4

4

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Inspect the flywheel/flexplate for the following conditions:

•	Looseness at the engine crankshaft

•	Cracks and/or damage

•	Missing balance weights

Did the flywheel/flexplate exhibit any of the conditions listed?

Go to Step 6

Go to Step 5

5

1. With the transmission torque converter still secured away from the engine flywheel/flexplate to avoid accidental engagement with the flywheel/flexplate, lower the vehicle.
2. Block the front wheels.
3. Apply BOTH the service brakes and the park brake.
4. With the scan tool and the J 38792-A Electronic Vibration Analyzer (EVA) still installed, start the engine.
5. Place the transmission in NEUTRAL or PARK.
6. Slowly increase the engine speed (RPM) to the level at which the disturbance is most noticeable.
7. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the J 38792-A .
8. Turn OFF the ignition.

Has the disturbance been significantly reduced or eliminated?

Go to Step 7

Go to Step 9

1. If the flywheel/flexplate is loose at the engine crankshaft, tighten the flywheel/flexplate mounting bolts in sequence and to specification.
2. If the flywheel/flexplate is cracked, damaged, and/or has missing balance weights, replace the damaged flywheel/flexplate. Refer to Engine Flywheel Replacement for the 4.2L engine or Engine Flywheel Replacement for the 5.3L engine.

Did you complete the tightening or replacement?

Go to Step 12

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7

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Re-index the transmission torque converter to the engine flywheel/flexplate, 120 degrees from its original position.
3. Reconnect the transmission torque converter to the engine flywheel/flexplate.
4. Lower the vehicle.
5. Block the front wheels.
6. Apply BOTH the service brakes and the park brake.
7. With the scan tool and the J 38792-A still installed, start the engine.
8. Place the transmission in NEUTRAL or PARK.
9. Slowly increase the engine speed (RPM) to the level at which the disturbance is most noticeable.
10. Record the engine RPM obtained on the scan tool and the most dominant frequency reading if obtained on the J 38792-A .
11. If the disturbance is still noticeable, re-index the torque converter again to obtain the least amount of disturbance.

Has the disturbance been significantly reduced or eliminated?

Go to Step 12

Go to Step 8

Replace the out-of-balance transmission torque converter.

Did you complete the replacement?

Go to Step 12

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9

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Position the J 38792-A sensor onto the underside of the engine oil pan, along the FRONT edge.
3. Lower the vehicle.
4. Block the front wheels.
5. Apply BOTH the service brakes and the park brake.
6. With the scan tool and the J 38792-A still installed, start the engine.
7. Place the transmission in NEUTRAL or PARK.
8. Slowly increase the engine speed (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 J 38792-A from the underside of the engine oil pan.
10. Repeat steps 1-9, placing the J 38792-A sensor onto the underside of the engine oil pan, along the REAR edge.

Is the disturbance greater along the FRONT of the engine?

Go to Step 11

Go to Step 10

10

Replace the imbalanced engine flywheel/flexplate. Refer to Engine Flywheel Replacement for the 4.2L engine or Engine Flywheel Replacement for the 5.3L engine.

Did you complete the replacement?

Go to Step 12

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11

Replace the engine crankshaft (harmonic) balancer. Refer to Crankshaft Balancer Replacement for the 4.2L engine or Crankshaft Balancer Replacement for the 5.3L engine.

Did you complete the replacement?

Go to Step 12

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1. Install or connect any components that were removed or disconnected during diagnosis.
2. Perform the Vibration Analysis - Road Testing table. Refer to Vibration Analysis - Road Testing .

Is the disturbance still present?

Go to Vibration Diagnostic Aids

System OK