Fleck

Car (2015 A8 Stingray z51) has 10k miles on it and i just had Texas Speed 1-7/8" headers an 3" off road x pipe, only thing else it has is a mild to wild for the NPP. Had a dealer put it on for me and they were fine with me driving it off the lot and going to a different tuner for a tune. So i immediately plugged in a OBD reader to make sure i was just getting 02 error codes which was all good, i believe there was 9 total codes all dealing with 02 stuff. I did take a couple recordings on the way home from the dealer(more on that below). It also dropped the mpg to 15-20 depending on how i drove it. I only drove it in manual to avoid v4 mode.

On the way home i could hit certain spots in the gears where it would make the engine stumble and felt like the rear end was hopping, halfway home a rear axle CEL warning popped up that went away after pulling over and restarting car so i plugged in the OBD reader again and there was nothing more than the 9 codes of 02 sensors. So i took a couple clips trying to record the stumbling and took it back home (shouldve went straight back to dealer now that i think about it!) and called the dealer, he said i can bring it in next week and have it looked at but he said they didnt touch anything that would mess up and cause a rear axle CEL randomly. So id like your guys opinions on all this, my two questions is 1. Is it stumbling because it isn't tuned? 2. Or is there a bigger problem causing it? Im obviously gonna let it sit in the garage and wait to get it tuned but im afraid something else is messed up.

Here is the bad clip

And then randomly it gets a good pull, but i know if i tried getting on it anymore it would have stumbled.

Tort

Not being a dick but.....you aren't tuned yet. What did you expect? Get it tuned and you should have no worries.

Fleck

I expected not to see a rear axle CEL while driving home..... This is why im on here asking, is the stumbling related to not having a tune or is something seriously wrong...

What if i wait the day of getting the tune and i go there to have my car breaking down on me thats not even related to tuning...

Tort

Don't kill yourself with the "what if" game. Either put it back to stock or get it properly tuned and report back. Installing mods that require a tune and then driving them without said tune is absolutely asking for issues and CEL(s).

BrunoTheMellow

Long tubes and no cats without a tune? Get it tuned and the tuner will also be able to tell if there's more wrong.

Or you may just have a loose plug wire.check them

Chazzmania

Yea so long tubes your gonna need a tune. So when I put my Kooks LT's on I had a lot of 02 CEL and a rear axle CEL. I guess it is common because my shop said they had the same issue when they installed LT's on the new C7. Now one thing they told me to check is make sure the shop or whoever installed the headers removed the spark plugs. People have tried to remove the factory exhaust manifolds and hit the spark plugs which can crack them. This happen to my car and it ran like ****, doesn't really sound like your problem. Easy way I found this out was removing each plug to see if there was a change. How's the idle?

Fleck

Idle is solid, have been told the car sounds healthy but obviously still needing a tune, love the sound, NPP and mild to wild I can make this thing quite but also make it insanely loud, didn't experience any drone, can't wait to get a tune and drive it more!

Internets_Ninja

Headers with no tune shouldn't cause the car to break up like that. I would start with the simple things like checking the plugs, plug wires, and O2 sensors.

Rear axle warning is odd, I would guess they are not related.

konqueror5

Ask the dealer what connections they pulled apart to do the install. I know for the passenger side it is suggested to remove the fuse box under the hood. Start there. I'm also going to suggest the obvious that you get it tuned. Why exactly haven't you yet? Warranty? Scheduling?...?

Fleck

Scheduling

Chazzmania

Yea it is an amazing sound with LT's installed. I am always opening mine up to hear the exhaust note.

Internets_Ninja

I noticed in the second video the traction control light came on. From my experience I've seen that happen before if the engine exceeds the ECU's torque limit setting. I don't see how you were on the throttle enough at that speed to break the tires loose.

The only way to tell is to datalog it while it's happening. I would be looking for Torque Management Advance kicking in and pulling timing back to try and not exceed the torque limit. If this is the case the only way to solve it is to tune the car.

Fleck

Got hptuners, hooked it up to the car and started it up and a grinding/knocking comes from the driver side, passenger cant feel it but can hear it at times when its loud.

Only codes its throwing is 02 sensor stuff, and i feel like something is seriously wrong or loose, i have a bad feeling its something with the drivetrain or engine but why would it not be throwing any errors??? Im scared to drive it and datalog it.

https://www.corvetteforum.com/forums...0300-help.html

my car is doing exactly what this threads OP was experiencing but im not getting any p0300 code..... Someone please chime in on this stuff,,, I have full access to hp tuners just not touching it because i don't think its related to tuning, shed some light to me as im very confused on whats causing this.

Internets_Ninja

Can you post a HP Tuners log of your car while you are experiencing the stumble? The first thing I would check is that the spark plug wires are not loose, are snapped down onto the plug all the way, and are not burned by touching the headers. But the HP Tuners log may help shed some light as long as your are logging the right parameters.

The good news is you're NOT getting p0300 which would mean a multiple cylinder misfire. This seems related to only a single cylinder or possibly a Torque Management issue in the tune. You need to log Torque Management Advance, along with all of the other spark multipliers and torque output PID's.

The grinding knocking sound could be the header flanges touching the tunnel plate. Have you been able to get under the car for a visual inspection? I wouldn't think you need to double check a shops work but I've seen it happen where they forget to tighten something or don't clock the header flanges correctly and it causes it to hit the transmission or the tunnel area. In fact TSP headers have been known to hit the tunnel brace even when you use the one they provide. Right around the Cat area. You might need to space the tunnel plate in the front with washers.

Fleck

Fixed part of the issue, one of the spark plug wires weren't all the way on, i dont see why or how but the p0300 code was never being thrown. This fixed the stumbling and back end hop but i still have a grinding noise coming from under the driver side part of the car, when idling up hill and slowly roll on the gas, the car will grind, almost like metal on metal gears grinding together, also happens randomly when shifting. Anyone have any ideas?

Forgot to add, it does it on cold starts too, so its not only doing this when its driving but even when sitting there idling it will randomly do it.

Internets_Ninja

I'm telling you, check the clearance of the headers under the car. It can sound like grinding. And it will likely happen most often during shifting as the drivetrain and engine move around a little during shifting.

I'm glad it was one of the plug wires as I suspected. And since it was only one and it was loose, you likely wouldn't get a p0300 code since that code is thrown when MULTIPLE different cylinders are misfiring.

Fleck

Yep it was the clearance on the headers, took it off and the pipe was grinding so hard together it looks like someone took a Dremel and tried adding enough clearance. Tsp headers with their tunnel plate had to plasma cut out a inch or two of it so it wouldn't hit. Glad I didn't just "take it to the tuner", instead chased my tail around on two problems that combined to make it seem like my whole car was gonna blow up.

Internets_Ninja

I've been around the block a few times. Glad you got everything sorted out.

falcon5619

Nice work. In my experience after a header install, you wind up with a cracked plug or loose wire. Some installers will remove the plugs first so they do not crack them while trying to wiggle the headers into place.

With HP tuners you may not get the misfire code but you can look at the real-time data and see which cylinder is throwing the most number of misfires and then track it down to that particular cylinder/plug.

Fleck

Took off a solid 2 inch's of the tunnel plate, so i start driving it and then it starts grinding near the x pipe part of the plate, so im leaving it for the dealer and im guessing the headers aren't tightened on the driver side or need it needs to be loosened and pushed up from the bottom and then tightened. ON TOP of that i get to a tuner and one of the 02 header sensors isn't reading so in hp tuners it was stuck on the same number so we get it up on the lift for like the 20th time in a week and the 02 is plugged in and no wires are fried and it still wont read it. So this whole time its been on a closed loop just dumping fuel because it couldnt calibrate anything. And on top of that the tuner wasn't willing to help replace a 02 wire, so i have to schedule another time once i get the dealer to fix all this ****.

Im not the one to shame a dealer and im trying to hold myself back from saying it, but what the ****..... How can you not check for all this? Every single problem ive had in this thread is related to the header install that they did.