How do i change the serpintine belt on a 1998 oldsmobile eighty eight?

Yes

Possible "crank position sensor", but also inspect the harmonic balancer coming apart, the back of it has the on/off window plate that the ckp reads for ecm functions.

check the belt tensioner, and pulley to make sure that the bearings are not going bad.

I would look into changing coil packs. When your coil packs go bad they tend to cut out as the engine warms up.

I want to say T-50. Trick: press a piece of foil onto head of bolt before you go to store...

this particular engine requires the removal of the engine mount in order to replace the serpentine drive belt i know it,s not fun but has to be done

I believe this is the 3.8

There is only one thought or answer.

Since 1980, whenever you get a check light on, you go to a repair shop. They check the codes, that set the light,and use that as a starting point, to diagnose and repair your issues.

First draw a diagram of the belt routing. Next have a 3/8" ratchet in hand. The ratchet will be used to insert into the belt tensioner 3/8 slot to releive the tension to the belt. Upon releiving the tension you can slip the belt off which is the easy part. Now reverse these directions to install the new belt and be careful not you pinch your fingers

check here
http://www.2carpros.com/car_repair_information/tec_info/1995/oldsmobile/eighty-eight/1995_oldsmobile_eighty-eight_drive_belt_routing_diagram.htm