R32R1

All (3) cats are stock, Corsa is your standard cat-back exhaust: Corsa Exhaust Site Start-up is nice and strong, no hesitation there. It cranks slightly longer than my other ones did, but I'm pretty sure that's the nature of the 6.2l since I remember thinking that to myself when moving a dealership Yukon 6.2l one day. I'm not sure why it was replaced since it was with the previous owner, and he had it done at another dealership. I noticed the papers when picking it up, but I didn't ask them to look up the details - just saw torque converter replaced. Yea I have a highly modified VW R32, and it feels similar to when I bent 3 valves in that thing. Granted, not as drastic or any CEL, but that memory never fades. What's weird about this is that when I picked it up, everything felt fine (for once). I drove a bunch, felt fine, plugged my Range AFM Disabler in, felt fine. I put the exhaust back on, felt fine after that! Driving about 100 more miles and I feel like a 4.3l can pass me at times. I spoke to my buddy at the dealership and he gave me the green light to use a tuner to see if that works; he used to tune C7 Le Mans cars in his past life and is confident it has to be software related. As long as I can bring it back to stock with stock emissions, they can cover it under warranty. I'm still hesitant on doing that, as I really want them to inspect the valves for any major issues like the AFM lifters screwing up. My gut instinct is telling me that I have a weak/cracked/broken valve-spring somewhere. If it's a stuck lifter, you KNOW it's a stuck lifter because it'll show symptoms at idle. But a defective valve spring can be deceiving at idle, yet when it really needs to work, that's when it'll show its true colors...then again, I'm not a tech and that's only a hunch

Spoke too soon...exhaust back on and it's doing it again. Not sure if it's coincidental, but something tells me I'll be swapping the exhaust back to stock (yet again) for them to look at this. Im starting to really dislike this truck, and that's the last thing I need right now. Symptoms are in 3rd gear and up, 40% throttle- I'll get the hesitation/ misfire feeling. I checked the maintenance records and this truck already had the torque converter replaced at 35k miles. All updates are done on it, so I'll try swapping the MAF to see if that's the cause.

Final Update: Dealership replaced the other (4) injectors and the truck runs perfect again. As for a cause, who knows...but at least the problem is solved. 8 bad injectors is a little concerning though... Exhaust and intake are back on Thanks for the help everyone!

Update- Truck is back to stock and still showing the same symptoms: Hesitation/ Misfiring/ etc I have a feeling it's something as stupid as an 02 sensor or MAF, or as serious as a cracked valve spring. It'll be going to the dealership tomorrow, so hopefully they can figure it out.

That's what I'm saying!!! This is my 4th GM, 4th Corsa (TBSS, Escalade, '12 Sierra 5.3, Denali) and all of them had zero issue with the corsa. Exhaust has no leaks or anything either, but I'm swapping the stock on so It's 100% by the book.

They mentioned something about the back pressure being off due to the Corsa exhaust and how the 'flapper' in the stock exhaust is what maintains back pressure. I get that if they bring the tech from GM in, there obviously can't be an aftermarket exhaust on, but is the computer that sensitive these days that it'll be thrown off by that?

Thank you, I am returning everything back to stock so they can properly diagnose it. Hopefully I'll have an answer this week and THANK GOD I didn't have to cut my exhaust off like we did on my old truck. Still in one piece and can easily be re-installed

Thanks lol

Ha believe me, it wasn't known when purchased that it was a problem truck. Coming from a 2012 Sierra 1500 5.3 SLE, seeing the Denali come in on trade was like a godsend. I'm friends with the owner and mostly all staff there. They definitely go the extra mile to assist, but it's also that 'think outside of the box' thought process that might help a little more with troubleshooting. I've spent many days in the waiting room with my other vehicles while mine was in for routine maintenance, and I've never seen another dealer treat their customers better than this one. Like anything, it's a business - I get it - when the book time is up and the warranty money for that ticket runs out, time to button her up and send it. I am just trying to provide them with a little more info, so they can attack this with a new ticket, new aspect to hopefully figure out the issue. Problem is my patience is wearing thin, and part of me just wants this engine to lean out and blow up so they have a concrete warranty claim instead of chasing a 'what if it's this'...

Hey guys, I've been a member of a few other car forums over the years, but recently decided to join here after hours of searching online with minimal results; hopefully others experiencing this issue can be armed with suggestive data for their dealers when going in for service. I'm no expert, by any means, but have tinkered on my VW R32 long enough to build it to 600hp, break, rebuild, repeat... I recently purchased a 2015 Sierra 1500 Denali 6.2l and have been experiencing 'misfire' like symptoms right off the bat while at 40-50% load (full throttle was fine). I knew about the 8-speed transmission issues, and the dealer showed me about 15 TCM updates that they can perform. To my surprise, everything from the slamming into reverse to poor shifting cleared right up, and the truck drives perfectly fine when driving like a grandma. We went on a test drive together and I duplicated the misfiring to him, while he read the ECM live. He saw 4 injectors not performing, so the dealer replaced those 4 injectors. While in there, he spotted coolant (common issue with the T-stat), and replaced the Radiator and T-stat under warranty. Within a week after that, I bought and installed the following mods: Range AFM Delete Corsa Sport Exhaust Corsa CAI EDIT** Returning back to stock for proper diagnostics. Now that I can actually hear the exhaust note, the 40-50% load misfire is still there, along with full throttle being painful. at 5-6k RPMs, I've had misfiring, backfiring, loss of power, struggling or 'confused' in wanted to shift to the next gear (truck held itself at 6k RPMs for 1.5-2 seconds) and honestly feels just like when I bent 3 valves in the VW. For the record, the dealership is a friend of mine and the service department is outstanding; they will do anything to help me out, and I'm trying not to be "that guy" when going back for the same problem. I believe the 4 injectors replaced were all on the same bank. Looking outside of injectors, has there been any known issues with collapsed lifters or fuel pump/line issues that they can possibly address? Thank you, Eric