2000 scsb 4.8l .513 lift crane cams and circle d 2500 stall. I bought this truck already cammed. All of a sudden, after a car wash, it started misfiring... i didnt open the hood during this wash. It went away after a few minutes. Next morning, about two months ago, and ever since it misfires about a minute after starting it so must be electrical is my thought. The misfire steadily fades as i drive and things get warm. Code was for #7cylinder. New plugs, swapped injectors and bought new o rings. Nothing. All new coil packs on that side. Nothing, still. Put in an intake manifold gasket, and flushed the intake out real nice. (Where it gets weird) started it up. #7 misfire code is gone. Then immediately had a random misfire code. And crank sensor code. Now, this thing will barely get out of its way, spitting sputtering, backfiring, jerking badly. Seems to run exactly the same, just worse. I erased the codes, and no matter how bad its misfiring and backfiring, no misfire code will show up. Just the crank sensor. Im at a loss. Tired of throwing money at this problem. At any rpm range, the timing is wildly up and down. Not sure if thats normal. At idle timing will jump anywhere from 12, to 40. Almost so fast you cant read it. Is the crank sensor worth doing? I cant afford to keep throwing money at this misfire, never hitting it. Anyone ever had the same problem,or could help me figure it out? New here, sorry if im doing this wrong...

 

Very well could be crank sensor issue, could also be the wiring have seen a few crank sensor harnesses that were overheated and burnt, and tge insulation cracked...

 

Alright. Thanks for the input, wolftrk99

 

Replaced crank sensor, now im seeing fuel coming out of the vacuum side of the fuel pressure regulator. Hopefully that part will arrive today... i fixed my loose battery terminals, which i thought were the cause of the computer resetting itself, but it wasnt, so every day it has to relearn to idle, and it wont throw a code before it resets. Its still misfiring, now its almost stalling put when i take off. Much worse. Cylinder 7 misfire code is gone, now its a random multiple misfire. Are these possibly symptoms of a bad pcm?

 

Yes, there are capacitors that keep memory alive, there should also be a constant 12v going to the pcm you really need to check along with all of your grounds before condemning the pcm though!!!

 

Cylinder 7 is notorious for collapsed lifters will def. give a misfire code!