1994 olds cutlass supreme ncar sometimes wont go into overdrive

Probably one of the guages are reading out of range.

launched it and this is going to give u an idea whats is happening .cutlass supreme are very easy to understand ..sometimes is a real failure or sometimeis a wrong action of your driving and ecu detected it as a fail.. be more specific please

Are you pulling a trailer or have a heavy load - you should not drive in overdrive in those conditions. You will eventually ruin your transmission.

Change CoilPack ! 2 possibility, Defective coil or Defective Module ( The Plate underneath your Coil ) ! Would go for Coil before changing the plate ! You can get some at Junkyard or New !

Could be .. did you do any voltage checks? I suggest you check altenator output as well as battery voltages under various circumstances.

usually means that you harrness is lose where it plugs into your fan check it you mite also want to clean the connecters

youve got a bad mastercylinder

It could be a broken wire going to the starter the little brown wire or it is loose.

When in overdrive engine is locked up with trans. so engine performace is more pronouced ,I would think a tune up would be in order.