Noise From Supercharger In Reverse - keywords clatter idle knock

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

The customer may have a concern of a knock noise or clatter coming from the engine compartment when the vehicle is in reverse at idle.

Because of the way the supercharger bypass is controlled , in drive / idle we are bypassing (no supercharger load) but in reverse / idle we are not bypassing (supercharger is loading engine) This load combined with the engine torsion causes the supercharger torsional isolator to bottom against its internal stops (limiters). This bottoming is what we perceive as the knock. Some engines seem to have slightly higher torsions and will knock in reverse. However with miles (break-in) the torsions diminish and the knock is lessened. Replacement of engine or supercharger will most likely not fix the vehicle.

This should be considered a normal characteristic and will diminish with mileage.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.