i am having a issue with a soft code on #8 cylinder and it is only missing at very high rpms. this is what i have done so far

changed all plugs
fixed various vacume leaks

my mods are somewhat aggresive cam, ported 243s boltons yada yada. i also installed a fast90/90 a while back. now the car ran fine after my head and cam install for months. so anyway, i installed the fast 90 and the car ran fine for a month or so, then all of a sudden BAM! car starts running like **** as described above. car is much better now that the leaks are fixed and the plugs are replaced i even did 3 wot pulls and no cutting out occured. the car is back to misfiring and i need to know why. my guess is fuel pump maybe since it is stock peice and i have heads and cam. do you guys think its fuel pump or maybe the inatke has somethin to do with it or maybe somethin else?

 

also my freind thinks it is a head gasket but i dont think thats the case

 

its not the fuel pump or it would be on more cylinders than #8.
did you do plug wires?

if you did not.

the cheapest way would be to swap out #8 plug wires with a diffrent cylinder and see if it follows or stays on that cylinder it will tell if the wire is shoot. if that dont fix it i would swap #8 injectors and see if that fixes that cylinder. if not then do the #8 coil with a diffrent cylinder coil and see if it follows or stays on the same cylinder. then after that it is for sure in the cylinder/head if none of them fixed it. i would do a compreesion and leak down after that.

and coils usually only screw up when warm compaired to cold but they still do screw up when cold

 

thanks for the reply, good advice i will try all those things in the morning. again thankyou

 

tt383lt1 thank you good advice

 

i would guess plug wire. if its not fuel and you have new plugs. what plugs did you use? i put autolites in my tahoe and got knock codes like crazy. went to a ngk 5 like i should have because thats what i always run and the problem never came back

 

i switched a coil and took it out for another test and guess what? it ran fine again, i even treid beating the **** out of it just to make the code come up and could not do it. but thats only cuz i had the scanner with me lol. next time without the scanner it will run like poo guarenteed

 

im running AC Delco iridium

 

Lean back cylinders ruin motors. I'd do the injector swap
and if that changes the misfire position then get them
reconditioned, the whole set.

 

update time, car has all new plugs as stated before. i switched over my coil pack with #5 and the wire from#5 and its is still doing the same ****.

 

i havent treid switching the injector yet, oops i forgot to try that