Originally Posted by dantheman1540

Is it possibly a crank relearn problem? Any engine codes?

Originally Posted by 00pooterSS

If it's backfiring or sneezing you have a cam or ignition timing problem, or stuck open valves.

Do a compression check, that will show stuck open valves and if the cam is far enough off the compression will be off across the board.

Check all wiring going to coils and verify each coil is in the right location. I had this whip my *** one time when a buddy pulled his coils, brackets, and wiring harnesses off the original valve covers and swapped them over to another set. He crossed some of the wires to the coils and my firing order was all over the place.

Another way to verify ignition timing is to make a mark on the damper for each cylinder TDC and hook up a timing gun and watch for it to fire on the mark, if it doesn't its firing out of time.

BUT I ALWAYS start with checking ignition and cam timing when it comes to backfiring on cranking.

EDIT: sorry just noticed you said you verified coil wiring and injector wiring for firing order.

Try disabling one cylinder at a time by pulling the injector connector and see if you can at least whittle this down to which exact cylinders are causing the back fire. If it's all of them I'd be looking at cam timing and reluctor ring orientation.

Does it have cam crank correlation codes?

One thing that helped me diag my buddies car was I pulled the connector for one whole bank of coils at one point and it ran perfect on the other 4 cylinders and wouldn't run at all on the 4 I had unplugged. That helped me at least narrow my focus to one side. Sometimes just having a smaller target is helpful.

Originally Posted by chris99gmc

I noticed you mentioned wiring as well... if you swapped coils or changed wiring for the coils, make sure you have them wired correctly for your Truck and the PCM for that year vehicle and PCM operating system. Not all LS vehicles have the same coil wiring configurations. I’ve ordered coil pack wiring harnesses before that ended up having the coil wiring backwards on all the plugs. If wires are correct, check to see if any of them are shorted to ground, including plug wires.

if it’s been sitting for awhile, check to make sure your injectors are not clogged up. This happens more than ppl think. Also make sure fuel pressure is good at the rails.

Since it won’t run at all, another suggestion might be the cam is 180* off.

start with the basics first. Mechanical first, electrical second.

Originally Posted by dantheman1540

I have those same injectors and they have been great in a magnusson but that's all I've had them in. DW supplies injector flow data did you send BBP the data? It's possible the injector data is off. But I agree it sounds like a timing issues

Originally Posted by 00pooterSS

It also struggled on starting on one of the cylinders, can hear it stop the starter then start again at 28 seconds. Something is out of time and by the way it runs it would seem it's one or two cylinders not all.

So I would really suspect a coil is hooked to the wrong cylinder. Unplug injectors and see which cylinder is causing it (unplug the injector so it doesn't shoot fuel in there creating a fire hazard on the out of time cylinder)

Doing one coil pack main harness connector will get you to the side of the engine that is doing it, hopefully it's only one side. Then you can go to each cylinder on that side and see which cylinders are off. If it's just 2 of them, then likely those two are swapped.

Originally Posted by 00pooterSS

Or do this

Unplug all injectors. Crank over engine to clear it out. Then plug one injector in at a time. When one causes an issue unplug it and continue on. Then see where you end up at the end with it running and how many are unplugged causing an issue. You want to kill fuel not spark so that you don't wash down the rings in your new motor.

If you pull one coil harness main connector unplug all 4 of those injectors also so that you aren't spraying fuel in an engine that is new, and also that is backfiring.