Engine Compartment Or Accessory Drive Belt Noise - keywords alternator cylinder deactivation mode pulley

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

Some customers may comment about a noise coming from the engine compartment when traveling at steady speeds. Some may also comment that the noise can only be heard when the engine is operating in the 3 cylinder mode (cylinder deactivation). Upon inspection you may find that the noise is coming from the accessory drive belt and that it appears to be jumping or whipping up and down only when the 3 cylinder mode is activated. When the engine is operating in the 6 cylinder mode the belt movement is smooth and the noise is not present.

Verify that the engine has the correct alternator installed. The alternator used on the 3.9L LZ8 engine (active fuel management) is unique and has a declutching pulley feature which is used with the cylinder deactivation. This alternator is not used on the 3.9L LZ9 engine or the 3.5L LZ4 or LZE engines. See the pictures below for alternator identification.

If you find that the vehicle has an incorrect alternator then you must contact Jim Kelly at (586) 492-5612 before replacing it. He will supply you with additional information and also the address of where to send the incorrect alternator to.

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.