Truck Mis-Firing

[BigMac]

My 08' GMC has been backfiring and hesitating pretty bad the past few days... I have no idea whats going on with it. I have tried HEAT fuel treater in the tank thinking I had water in there... no change. Its been down to 18* or so recently, when the cold weather hit is when the truck started running poor. Today the sucker backfired and blew my CAI off. All I have is a tune and CAI, no major mods.

[Frenchy]

How do the plugs look?

[BigMac]

I haven't pulled them, the truck only has 40k miles

[Frenchy]

Well pull them, spark plugs will tell you more about how your engine is running than any electronic gadget. My guess is it's too lean or too much timing.

[BigMac]

I was planning on checking them out as soon as the temp here gets over 20*.... I don't have a shop or anywhere to work out here. Thanks for the input.

[EmmerichLSx]

Same thing is happening to me in this ridiculously cold weather. It's a single damn degree outside right now lol! Plugs are a good place to start.

[BigMac]

Pulled plugs, they look fine. Now the truck only mis-fires and cuts out under WOT. I plan on putting in 48lb injectors soon but would like to fix this beforehand.

[farmtruc]

... My guess is it's too lean or too much timing.

Not to start nothing, so don't take it this way, I just think it's funny to come to this conclusion right off the bat. I would have started out with - history on the truck, any parts changed out, any ses lights maybe?

Now why would you say there is too much timing? The only way it could be too much timing is by the tune right? I would think I would know better to set the tune up with too much timing lol.
He would have known this right away after the initial tune install, he would hear detonation going on.
Seriously though, I'd like to know how too much timing could have happened or caused this?

Now running too lean, that could be anything, so I won't say you were blaming the tune on that one.
It could be lean, maybe a bad fuel pump?

Steps:
Did you change anything recently?
Get fuel pressure checked.
Maybe get the pcm read regardless of ses light illuminating, see if there is something in history.
Check to make sure the O2's are toggling correctly. O2's don't set right away, maybe it's a semi-bad O2.
Get the truck scanned and view all cylinder misfire data. See if any of the cylinders are misfiring.

Those are some of the first steps I'd take.

I'm thinking a bad o2 sensor.

lmk,

allen

[farmtruc]

Pulled plugs, they look fine. Now the truck only mis-fires and cuts out under WOT. I plan on putting in 48lb injectors soon but would like to fix this beforehand.

I just saw this, only WOT? Check fuel pressure under a load/wot.

[BigMac]

I'm running my gauges for the turbo setup so I'll go ahead hook up the fuel pressure gauge. Dealer replaced an o2 sensor today and it fixed the mis fire, it still cuts out under WOT, feeling like no fuel so I'm thinking low fuel pressure. Nothing wrong w/ the tune, it just feels like its not getting enough fuel. Thanks for the help!