GMC SKI

well a few weeks ago had some issues with the truck running really rough and felt like it was missing I scanned the truck and it came up with a cylinder missfire code .I changed the plugs out for a new set of NGK tr6's and it was better smoothed itself out. today went out for a drive and it started to do the same thing rough idle no engine light yet ..what could this be maybe a bad coil pack ?my plug wires are new msd's
Could too much fuel make this happen any thoughts on what i should try next ? I don't have Atap and where i got it scannend my buddies shop he just has a simple scanner
I don't wanna go to the dealer
but i might have too
Can i unplug plug wires while the truck is running to figure out which cylinder it is that is running rough or will i do damage doing that ?

jim

WILWAXU

iTrader: (5)

Moving to the Truck section.

z71tahoe

Jim,

Ben here. I had the same problem (I hope) it was 2 of my coil packs. I think they got wet some how. The truck actually felt like the motor was dying- I drove to the local auto zone and the guys there swapped out one from there truck- only to find out it got a little better- 1 more and I was set- set on driving to the dealer and buying 4 extras and 2 new ones for my friends at autozone.

I trie your other theory about the fuel pressure- My truck sees 50psi of fuel at idle but i can adjust it up to 80psi. from there it is a linear increase i successfully got it to idle at 70psi and I did not experience your problem- I do think I ran through about a 1/4 tank on the 5 mile drive. No notice of improvement either- BTW do you know what fuel pressure you run at idle?

Ben-
Z71 Tahoe page

GMC SKI

did the coil packs give you a cylinder missfire code
the things runs rough with a heavy smell of fuel coming out the back
hmm gotta check the coil packs

z71tahoe

Yes Yes Yes. I got the cylinder code- and It did smell like gas but remember a SC truck will smell worse than a normally aspirated vehicle (under boost). I was scared I was going to blow up.

Check your code read what cylinder is misfiring. Clear the code and switch packs with another cylinder- See if the code changes to the other cylinder- it will if it is the coil pack- Then buy a new one. if not ...... Well it could be the fuel p regulator, infact I broke the diaprahm in my ATI fuel back pressure regulator. The hose blew off and I lost 2 gallons of fuel in 30 secs plus I almost blew up- You will have to know your fuel pressure real time to diagnose this. I spent a great deal of time re-engineering this problem- I would be glad to help out any way I can. just let me know and feel free to ask any questions-

Just be careful- Fuel vapor is deadly -

ben

Let me know how the ls1edit works.

JWRENCH

If you don't have a scanner handy, just pull your spark plugs and check them out for raw fuel, etc. That'll tell you exactly which and how many cylinders are involved and wheather it's fuel or spark related.