my 2001 impala needed a new belt, but when I put it on (following diagram correctly) it jumps off every time I start the engine....what am I doing wrong?

 

It's the 3.4 engine, and all pulleys move freely, no wobbles. They do not all line up exactly (but thats how they were when the old belt was on) theyre within 1/4 inch of each other. The tensioner pulley rests on about 1/2 the belt (again, how it was on the old belt) Any suggestions???

 

Welcome to the forum. It sounds like you have your answer, i.e., pulleys are not lining up. I assume the previous owner botched something. Rent a pulley puller/installer kit and then fix the problem. You may also need to replace the tensioner assembly.

 

what im not understanding is.....if it is the pulley alignment, how did the old belt work without issues for so long? just luck?

 

If it got you stumped when you're standing there, there'd be no way for me to tell. How long has the old belt been there and what's its current condition? Did you compare the old one with the new?