This is the fastest way to remove the serpentine belt on a 4 cylinder Fiero Iron Duke engine. No need to remove the alternator, brackets, or any pulleys. 30 seconds or less. Use a 15mm socket on the tensioner bolt, and rotate clockwise.
The tensioner just pivots moving the pulley and creating slack in the belt. Do the opposite to put on a new belt. 85’ 2.5L engines and maybe others have different tensioners. I hope this helps.