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Hi all. Well I'm back with another difficult diagnosis. At least it is for us "Newbies" Allmost got it narrowed down to either the ICM or PCM, or wiring issue. Both the ICM & PCM & CKP have been changed. Tipical parts changer BS!... Anyway the Grand Prix will just quit at anytime uzually after warming up and doesnt matter if it's under a load or not. Usually start right up. But it finally wouldn't on me the other day and of course I didn't have spark then did and ran again for awhile till stalling again. The CKP had signals output but no spark... I varified + & - through the ICM already but not through the PCM. Now the owner said that there is a connection coming from the PCM that switches from 12v to 5v after it starts, but watching our Leader explain it it doesn't switch from 12 volts to 5 it begins its 5 volts. After 200 RPM the PCM takes over and controls the spark. I see that in the wiring diagram, there's a bypass connection from the computer and I assume that is the one which takes over. ?. Thanks for all help. Doug.
yes there is a 5 volt reference circuit for the sensors the crank sensor is on that circuit i would watch my rpm and see if it at least bumps and works when driving other than that it kinda sounds like your crank signal is dropping out maybe intermittant are tuff sometimes
