GM Service Manual Online
For 1990-2009 cars only

Heavy knock hot with torque applied may be caused by one or more of the following conditions:

    â€¢ Broken crankshaft balancer or pulley hub--replace the components as necessary.
    â€¢ Loose torque converter bolts--tighten the torque converter bolts and/or replace components as necessary.
    â€¢ Drive belt(s) too tight--adjust the drive belt tension to specifications.
    â€¢ Drive belt(s) nicked--replace the drive belt(s) as necessary.
    â€¢ Exhaust system grounded--reposition the exhaust system as necessary.
    â€¢ Engine flywheel cracked--replace the engine flywheel.
    â€¢ Excessive main bearing clearance--replace the component(s) as necessary.
    â€¢ Excessive rod bearing clearance--replace the component(s) as necessary.
    â€¢ Low quality fuel--fill with the proper quality fuel. Refer to Engine Controls.