Hey guys, I need some input on how to get my truck back in good working condition.

Background: The truck is a 2015 midnight edition Silverado 1500 5.3L. I had a procharger installed on it through the dealership along with the canned procharter tune. It ran well for the first ~9 months and then a rocker arm broke (cyl 4 I believe) due to a manufacturing defect. In the process we discovered that the tune was severely screwed up. Brought it to a local performance shop to get a legit dyno tune. They weren't able to get it to rev over 4200 rpm without it misfiring and having "spark blow out". The shop tried just about everything. Gapped the plugs down, used a different coil pack, swapped the fuel rails to see if the issue followed the fuel. No matter what they did cyl 6 would have a misfire. So I have been babying it to and from work while I try to get the issue sorted out before bringing it back to have it tuned.

Symptoms:

The truck will intermittently lose power during acceleration. The entire truck will shudder slightly when this is happening. During this time, the check engine light will flash and the traction control warning light comes on. The traction control light goes away after a couple of minutes and the CEL will remain. It gives a code P0306 every time. Occasionally there is a throttle position sensor code "performance out of range" (I think) code that is also thrown.

Occasionally, when i start the truck it will start more roughly than normal and the S/C whine will be more pronounced and will oscillate a little bit. When this happens I know that the misfire will happen at basically all RPM or %throttle.

If the rough start does occur, I can turn off the engine and restart the truck and usually it will start normally. Sometimes if I accelerate hard and the misfire starts, I can stop and shut the truck down and restart it and it will also resolve the problem.

After a misfire the s/c whine even at idle can be louder than normal and make an oscillating noise similar to the issue w/ the rough start.

Also after a misfire, the truck seems to shift much harder. This is especially bad in the 2-1 downshift. It feels almost like I have a trailer with a brake system that suddenly engaged. The downshifting issue goes away when the engine is behaving normally.


Do you guys have any thoughts on what is going on? I'm running out of ideas.

Thanks,
Specter

 

have you done a leakdown test on the #6 cylinder?

 

The performance shop had tested the compression and said it was good. I was considering testing it again myself although it might be a bitch to do.

 

A compression test is not a leak down test.

 

****, just go out there and pull the plug and post a pic. It may be a dead give away at that point.