1990 Pontiac Grand Prix.. running in the FWD Pures at Springport. 3.1 MPI (not a 3100)

Engine cold, Car starts and runs good.

Take it on the track.. for the first 5 to 10 laps.. runs good, pulls strong.

After about lap 10.. motor starts to develop a miss.. few more laps motor will barely keep running.

Pull off.. let car set 15 to 20 minutes.. start right back up. But miss comes back more quickly.

Any ideas ?

do you have a spare coil that you can swap out? sounds like its more closely related to underhood heat... even though heat will go up for a bit after key off with the hood closed (in certain areas)

try ducting some air to the coils if you dont have a spare and see if it will last longer.

internal resistance of those things goes way up when the heat goes up, can cause weak spark or no spark at some point.

i would also check the spark plugs. if they are fouled, check your battery ground and make sure it's grounded good. to the block would be the best

steve "pops" pastorino

Put a fuel guage on it. The pump bearing would tighten up when hot, not sure which years.

Pull out the crank sensor and see if it has any cracks on it, If it does, replace it. It,s on the back side of the block, near the bottom and about 3/4 of the way forward. These engines also have injector woes, and the easiest way to check this is to check resistance on the injectors when HOT, all readings should be close to each other. 1 bad injector will foul the signal to all injectors. BTW if the crank sensor won't come out, its cracked and oil swollen. DON'T break it off in the block. Major PITA to remove. Any ? feel free to call me Jeff 989-345-5624

if the crank sensor is swelled CAREFULLY heat the block around the sensor and SLOWLY twist and pull reheating as necessary

It turned out to be a bad EGR valve.

Thats weird. It should have raced fine and only had idle issues with a bad EGR, unless you had that digital 3 valve junk one and all 3 valve were stuck open.

It was the electric EGR.. we replaced the coil pack first and it didn't seem to make a difference.. small, but not really.. then did the EGR and the problem went completely away.

Thanks to Derek Lacey for the tip.