C15 Acert backfire when cold

Have been having problems for about a year or so now with my C15 Acert backfiring when cold until it gets to full operating temp after running down the road for a bit. Traced it down to a bad injector, which was replaced, and also had the valve lash reset/adjusted.

Got it out of shop and still does the same thing, although not near as bad. Its most noticeable in the winter right away in the morning until like I said you get it up to full operating temperature after moving down the road.

I always start it up in the morning, let it build oil pressure and set a fast idle and let it warm up that way for 20-30 minutes before taking off. At that point engine temp is usually around 120-130, sometimes maybe as high as 150. Its ok when you first take off until you get into high range and really start to pull the motor with each gear change. At about 1300-1500 rpm you get a jerking/bucking. Will do this until motor gets to 180-200 in temp.

And the colder it is outside the worse the problem is despite engine temp. At 130 degrees engine temp its worse when its 15 degrees outside vs 30-35 degrees, which is worse than when its 50 degrees out and so on. But once the engine is warmed up for the day it runs just fine. And it will give this problem loaded or empty but probably more noticeable when loaded.

Is it still an injector problem? Something else in the motor/drive train?

 

Well I guess I'll describe it as a backfire, that's what it acts like and when I had a mechanic ride with me he put it that way. But let's just say there's a jerking and bucking like the engine is cutting out when its doing it. A bad injector was found and also someone had "attempted" to work on/replace all the others at some point...found out they were all out of order and set to the wrong cylinders. Fixed that problem as well. But like I said all the injector work did help, its not doing it as bad now.

And if its head gasket related would I possibly see it leaking somewhere or start to see some coolant showing up in the oil? I'm seeing none of that

How much of a job I'd a VVA? Honestly I'm surprised the mechanic didn't check for that anyway, he's quite picky at checking EVERYTHING. But I don't think there's any codes coming up so maybe he did and just saw nothing. but I can run this idea by him.

Honestly I'm about to sell this truck. I bought it a year and half ago and all I've done is beat my head against the wall ever since. Whoever had this thing before me wasn't big on maintenance and plain just ruined some things due to lack of and let some things just keep going that should've been replaced long before I bought it. Not sure if they were doing the work themselves or had a mechanic but whoever was doing work on it should be shot. Of course the place I bought it from did a good job at hiding and covering a lot of stuff up.