The cam is fine...he's not billing me for any of the diagnostic work at all. It's quickly looking like either a full engine autopsy needs to be done or scrap it and put a brand new engine in the truck.

 

odd. so it all started with a miss fire they did plugs checked for spark and checked fuel injector. they did heads and valves and cam is fine. did they check lifters and push rods? compression was good too no?
are you sure the mechanic does not want your engine for a side project because nothing adds up. unless the engine is fine and you have harness or sensor issues or a plugged exhaust.
maybe all you needed was a crank relearn.

 

I find it so hard to believe an LQ4 with such low mileage has these kind of problems. I rummage through junk yards all the time and it's not uncommon to see LQ4 GM work trucks with close to or over 300k on them.

If it truly needs and engine consider purchasing a long block from summit, they usually require a core (which will take the old LQ4 out of the picture if you mechanic wants your engine for a side project) The replacement are offered in various flavors starting around
4K with a warranty. You can go mild to wild, its up to you and your wallet. You can also purchase a genuine GM directly from them at around 4,6k

Bottom line, you do have a number of options, purchase a new/rebuilt LQ4 or get a second opinion on the findings (this might be a bit awkward without having the H2 taken to a different facility)

It seems you are at the mercy of your mechanic, I just hope he is competent and honest. Best of luck in this tough situation.

 

This is old news(est. 2000) yet still the FIX!😎
Bulletin No.: 16-NA-383

 

Unbelievable! So there was nothing wrong or excessively worn on the timing chain, or where the lifters tested? guessing he's not putting it back together? and why Crate change it and not rebuild the bottom end since he already had you allegedly did the heads rebuilt? also if he is not finding the problem in the motor, wouldn't that lead back to ECU problems or Sensors Cam/Crank/knock.

Like this bulletin although i believe its oil residue that causes the build up rather than the fuel, We will see I am installing an oil catch can to see how much is going up through the PCV line.

 

Here is the update:

As it turns out the rings are shot and the cylinders are scratched, so the motor is garbage. Every test known to man was run on this motor and before we ordered a new one to be built it was completely pulled apart and this is what was found. After all of the trouble shooting trying to avoid putting in a new motor, I'm having a new engine built for it. With parts on shortage it will be about 4 weeks until the new motor is ready to go.

Before I ordered the motor I had a chance to speak with a former GM Master Mechanic...he asked me if the coil packs and injectors were moved around to see if we could duplicate the issue in some of the other cylinders. That was one of the first things my guy did. I told him "yes, he's tried to move the coil packs and injectors and the problem is still in the same cylinder" If all other tests were good and Cyl 3 keeps failing there has to be an issue within the cylinder (which there was) or the block has a small crack.