I bought a used 91 Bonneville LE 2 weeks ago and it's dead. When it WAS running, had 4 sensors (cam sensor and transmission sensor plus two others) replaced and it helped, was running rough. Then, it started stalling when making right turns. Found out that one of the engine mounts was missing it's bolts. That helped. Then, it died in the parking lot; got it jumped and went straight to the auto store. The alernator was fluctuating on the output. Also, the turn signals flashed VERY slow and the fuel gauge would bounce back and forth between 1/4 tank. So, I replaced the serpentine belt, idle pully, and alternator (the idle pully had holes and was chewing up the belt). It ran better than ever. Then, 100 miles later, the temperature light came on the dash, but the temp gauge did NOT go up, and the engine stalled. When I turn the key, I get one quick click and that's it. The battery is charged, tried jumping it and smacking the starter and nothing. The radio, etc still work. I've had starters do this before, but never heard of one where it stalls the car. Is it one of the computor modules? After owning the crap car for 2 weeks, so far I missed 3 days of work and am currently having to borrow a car. Any help would be really appreciated.

okay dued it sounds like you did alot of work to your car that should of been taken care of a long time ago. anyways those engines are not desinde to withstand hi heats (they have alluminim heads). which isnt bad but tend to warp easier. anyways to help out some, if your starter is just going thunk, thunk, likes its engaging but not turning the engine over your screwed. its more than likeley seezed up. sorry i cant spell. if it turns over but does not start then.
1. smellyour oil. if it smells like gas then check your head gaskets.
2. if theres water in the oil its head gasket
3. or it may be something small.
check spark plugs
wires
coil packs
and maybe fuil filter
thats all i have to offer good luck.

I know it's a little late, but maybe this may help someone. I had very similar problems on my '89 and it drove me crazy. It ended up being a ground wire from the engine to the body of the car. Not your typical battery ground, but about a 3/16" wire from the alternator bracket to the body on the passenger side. Hope this helps someone.
OP

i have a 98, and just the other day i had the same experience.. the car stalled and the starter cant turn over the engine. i opened up the engine to discover water in the engine. and a crack in the head gasket. what a pain in the ass that was getting to it. that explains why garages charge so much to replace it. anyways when theres water in the pistons the engine will not turn over to much traction. replace the head gasket and everything will be fixed. as long as theres not too much water in the oil then its not that bad. in my case the water was contained in the engine and the car never overheated, as the water getting into the cylinders was actually cooling things down and preventing combustion.

hope that helps
RO