The 3.8 Liter Engines diagram is posted below.
Remove the air intake line from your engine.
Using a hex-head socket on the tensioner pulley, rotate the tensioner clockwise and slip the belt off of the pulleys.
Slowly release the the socket making sure not to let go to fast that the tensioner snaps back to fast.
Inspect all pulleys to ensure they are not damaged and are free of any fluids and/or debris.
Using the correct diagram provided, wind your belt around all of the pulleys leaving the tensioner pulley for last.While maintaining tension on the belt with your hand, rotate the tensioner enough to slip the belt over it.
Double check and make sure you have the belt on all of the pulleys correctly.
Replace your air breather.
It would also be a good idea to check the tensioner and make sure it is providing enough tension on your belt. The belt should have no more than 1 inch of play.
3.8 Liter Engine