I have a 99 Lumina, 3.1L v6. This has been an ongoing problem for some time. It seems to be heat related, in that when the weather is cool, it seems to run fine. When hot, you can be driving at most any speed for 80-20 and the car will shut off, engine quits....although when you pull over it sounds like it is pre-igniting like older cars used to do. If you let it sit for a bit, it will restart, and sometimes run fine for weeks, or it will be ongoing for the next several hours. I have replaced the Ignition Control Module, and coils, and all seemed to be well, and now it is ongoing again. A mechanic said I needed to replace the ECM, which I will do if that is the problem. Any help would be much appreciated.

i think computer is telling it to shut down..have you replaced the cps??? if so i'd go for the ecm..

You didn't mention the fuel pressure at the time the vehicle quits.On most GM vehicles if the fuel pump quits and leaves you stranded you can restart it by smacking the bottom of the tank with a rubber mallet.I would also check your catalytic converter.If the law is tolerant in your area you might unhook the exhaust at the manifold and drive it that way for a few miles to see how it acts.Another alternative is to make a pie cut ahead of the converter with a hacksaw.It's much quieter and can be easily repaired by an exhaust shop later for $20-$40.Good luck!

The only reason I think it is electrical, is the heat thing.....on cool days like this morning, it runs like a new car and you cannot get it to shut off. I drove it 90 miles one way yesterday afternoon...was fine, turned around to come home and it was the drive from hell. Sometimes you could go 20 miles on the interstate....it would quit and then it was every 2 miles.

I also forgot to mention, this has been an intermittent problem since this car was brand new....I bought from a relative so I know the history of it. Has been to the dealership several times, and they could never find anything wrong.

there's a plastic wire loom that splits from a larger main harness near your intake, runs between the engine and the dash firewall, goes down below your backside sparkplugs to a ckp (crank position sensor) sensor in the side of your engine above the oil pan, make sure it hasn't been burned and shorted by the exhaust. I had random shutdowns when the wire insulation was soft enough to allow a short.

Unless you are specifically looking for this problem, you won't ever find it.

last I heard a CPS is a camshaft position sensor. CKP = crank pos sensor.