Low oil pressure.

Perform an oil pressure test. Refer to Oil Pressure Diagnosis and Testing .

Detonation or spark knock.

Verify the correct operation of the ignition controls system. Refer to Diagnostic Starting Point - Engine Controls .

Loose torque converter bolts.

1. Inspect the torque converter bolts and flex plate. Refer to Flex Plate/Torque Converter Vibration Test for 5L40-E/5L50-E or Refer to Flex Plate/Torque Converter Vibration Test for 6L50/6L80/6L90.
2. Repair or replace, as required. Refer to Torque Converter Replacement for 5L40-E/5L50-E or Refer to Torque Converter Replacement for 6L50/6L80/6L90.

or Refer to Engine Flywheel Replacement .

Cracked flywheel - automatic transmission.

Repair or replace the flywheel. Refer to Engine Flywheel Replacement .

Above acceptable connecting rod bearing clearance.

Inspect the following components and repair, as required:

Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .

Above acceptable crankshaft bearing clearance.

Inspect the following components and repair, as required:

Refer to Piston, Connecting Rod, and Bearing Cleaning and Inspection .