I have a Cylinder 1 misfire on my 2008 GMC Sierra 1500 5.3L. It has 115k miles on it so I replaced the wires and plugs thinking that would fix it. It didnt. It is stumbling, riding very rough and jolts when changing gears.

After searching and not finding cylinder layout on this engine, I stopped by Firestone and asked them if they knew where cylinder 1 was...they said driver side front. I purchased a new coil pack and installed it on what I was told was cylinder 1 but that didnt make a difference either.

Can anyone help diagnose this issue and verify where cylinder 1 is?

Also, very strange but as soon as the check engine light came on and started stumbling (like a bad plug/wire) the Service Stabilitrak and Traction Control light came on and wont go away.

Thanks for any help with this.

 

Have you considered doing a compression check? Might not be ignition but a internal parts falure..
Num.1 cyl is front drivers side..

 

easiest way to find cyl 1 on just about any v-layout engine is look at which head is closest to the front (they are offset)

swap the cyl 1 and cyl 3 (the one next to it) see if it the missfire code moves...
^^^^ if that doesnt do anything then keep reading lol

+1 on the compression check... compare it to another one...
if its odd, pull the Fuel pump relay and spin it over until it stops trying to crank..
pull the valve cover and have someone spin it over and see if both of the rockers are moving (it may take a few seconds of spinning)
If it doesnt move or the rocker has alot of slack b4 your spin it over then your in need of a cam and lifters (becoming common on the AFM truck motors)

----another sad clue would be a ticking noise at idle from that corner, and louder on start up....