Holty

iTrader: (6)

not following you here on this one Julien?

Atomic

iTrader: (42)

Assuming you still have the PCV system routed to the intake, if you are having lots of blow-by you will suck up a lot of oil into the intake, and oil in the intake can cause misfiring...

Holty

iTrader: (6)

Oh ok, i gotcha now. I have converted to a catch can setup years ago though so no pcv to the intake.

Spoolin

iTrader: (8)

Ahhh, bummer. It was the one thing that I saw you hadn't checked yet. Then again your plugs probably woulda shown signs of that. Back to the drawing board...I'll keep thinking.

Spoolin

iTrader: (8)

Ok...check your engine wiring harness, especially the loom by the drivers side tire that leads into the PCM for bite or cheweing marks. If your coils, plug wires, spark plugs and what not have all been swapped a million times than it's gotta be a faulty signal prior to that, inbetween the PCM and the coils. Shot in the dark but you don't have any vermin problems do you?

Fastcount03

iTrader: (13)

Or a dog??? LOL

Gadgetized

iTrader: (9)

Another thing that was running through my mind was your injector wiring. I am not sure if it would cause your symptoms, but it would be pretty easy to accidentally switch your plugs around for #1, and #3 injectors. I would obviously check all of them to make sure.

Holty

iTrader: (6)

OK, Julien, i have not had a chance to check the wiring into the pcm yet, but i think about this **** at least twice a day and the more i think about it the more i am leaning toward a bad/weak valve spring.

Reason (in my mind): what causes backfires? exhaust valves not closing, or not closing fast enough, right?

OnyxSilveradoSS

iTrader: (4)

man I feel the same way about my truck...

hope you can keep motivated to figure it out.

03sierraslt

iTrader: (22)

This thing has me stumped... Rode in it tonite, its a bad misfire for sure.