QUIKAG

Can any of you track day guys and/or tuners please help me identify what is going on? It's not the microphone, it's some sound difference in my exhaust. It "changed" towards the end of this session and sounded the same way in my next two track sessions. It also sounded the same driving around town tonight.

It kind of sounds like maybe an exhaust leak or an engine miss? I have no CEL's or other issues on the display. I plugged all 4 of the pipes in the back for a minute and couldn't hear a hiss or anything further upstream of the exhaust, but I know that's not a fail proof test. It also doesn't seem to have any noticeable performance loss.

Please listen to a couple of lower rpm accelerations in the middle part of the video and then a couple in the last few minutes of the video. It's really strange. The car goes from a tighter sound in low/mid range of the rpm to sounding more like a pick-up truck with glasspacks. Car still pulls hard and it ran 'fine' for rest of the day?

http://www.youtube.com/watch?v=ZXPPKEqFea4

Any help would be appreciated.

3LZZ06

Thanks for sharing the video.

I watched the whole thing and it sounds like just before 14:00 minutes into it the car started missing a beat. Hard to pinpoint though. If a plug wire came loose you would certainly see a CEL...hmmmm strange.

I could hear the torque management doing it's thing throughout the video. Maybe excessive heat pulled a bunch of timing?...Did this same exhaust sound continue after the car cooled down?...

range96

I noticed a big difference in the sound between the beginning and the end. It almost sounded like your engine was missing and was down on power. I would pull the plugs, check them and do a compression test.

Good save on a few snap oversteers.

whatcop?

Possibly you broke one of the cats. You will know tomorrow when you start it up cold and it spazzes out and throws a CEL.

QUIKAG

Yes, the same exhaust sound was there after I brought it home, washed it, cooled down, and then I went for a drive. I like 'whatcop?'s' theory of a broken cat as that seems the most plausible. It hasn't broken enough yet for the CEL to show up?

I don't like range96's theory. It really doesn't seem down on power at all and it still pulls hard, it just sounds different. Like a little more boom/bass in the exhaust and a more stacatto sound.

C5 Hardtop

It sounds like your tires are worn out and the traction control is working now at times where it didn't before. Were the driving aids off all the way?

Easy way to tell if its the computer is to reproduce the problem, turn AH and TC off then try to reproduce the sound again.

Short story.. I thought my 6k mile LS3 vette had worn its clutch prematurely because I felt slippage in the upper powerband 800 miles in on a 2000 mile road trip. It only happened when I dropped down to 3rd to pass people.

It was just the tires slipping that made me think it was a clutch issue. Couldn't believe the car had so much power it would spin the tires at 75 MPH, but that was the problem.

Shurshot

Pull the valve covers!!!

If something is not obvious then with someone else to help you with oil splash shields start it up, watch & listen.

That is a "standard procedure" for other HP motors when the exhaust note changes.

Unless there is a specific LS9 reason not to do this, this is what I would do.

Good luck

QUIKAG

I had the computer in Race mode 5. The tires were worn out and the performance traction management was kicking in quite a bit more. I still don't think that is the cause of my engine note change as it will do it even at lower rpm in a higher gear where tire spin is basically impossible, even with worn sport cups.

By the way, I got less than 4 track days out of my sport cups. I drive pretty hard, but that's pretty dramatic wear for my tastes at $2k a set. So, I'm going to go back to the PS2 tire. They're about 85% of the grip of the sport cups and gets 4 times the life (for me) for around the same price as the sport cups.

QUIKAG

If the car wasn't under warranty, I'd pull the valve covers, but seriously it idles and drives perfect, it just has a different exhaust note under heavier throttle. It's weird. I just got back from a 45 minute drive all over some local tollroads here in Dallas and if anything, it pulls HARDER than it did before yesterday. Maybe, I broke some internal baffle in the exhaust and it's added 20hp or something? haha.

Car runs perfect, the exhaust just has a different tone/pitch more of a growling exhaust tone versus a snarling/higher pitch shriek type sound. It's odd, but the car really runs as strong as it did before, if not a touch stronger...

Before my drive, I unplugged the battery (I figured why not?) and put the car up on ramps/jack stands and crawled around underneath. I wiggled, tapped, and pushed on everything and everything seems perfect underneath. No exhaust leaks noticeable, I tapped the cats pretty hard and didn't hear any rattles or anything indicative of it breaking up, etc.

whatcop?

I agree with a baffle or cat theory. When you had it up in the air did you turn it on and listen to it at idle? If not I would suggest doing that.

kingofbikes

Sounds like engine miss... could be due to number of things from exhaust issues on the tune or broken or stuck roller rocker.. needs to be looked into...

range96

You may not like my theory, but pulling the plugs and checking compression is still prudent. I'd do it just as preventive "maintenance". People tracking their cars should do it at least once a season.

I would imagine a broken cat would throw a code.

Popping the valve cover is a good idea, too. Even without starting the engine (and create a mess) you could still visually inspect the rockers.

If these things don't reveal anything I would seek "professional" help.

Regardless of the outcome please report back for everyone's benefit.

I hope it is something stupid simple.

fisher auto

Could be a blown muffler bearing, pull the motor and do a rebuild.

Gary '09 C6

I'm no expert, but possibly a broken/damaged spring that attaches to the butterfly valve in the exhaust ?

QUIKAG

I'm starting to wonder if it could be the microphone. It shifted a little and then got some dirt in it? Who knows. I just hate to take it to the dealership for a slightly different sound under WOT and then have them go do their own testing for 25 miles and not notice anything out of the ordinary. haha.

She hasn't been to the dealership yet since I bought her, so I'm not too inclined to run it over for something that may be hard for them to detect. I don't have the knowledge or tools to do a compression test and I don't feel like touching the engine (besides oil changes) while it's under the 100k powertrain warranty.

I'll call over to the dealership and see what they think though.

VasMan

I just broke one of mine. Sounded exactly like that. Watch for pieces trapped in the exhaust Maffler Baterfly, particularly when you switch to mild (mild to wild) and the butterfly opens and closes.. It will get it stuck.

jvp

I'm going to be the answer to this is, "No." Did your car illuminate the CEL when that happened?

jas

whatcop?

I am willing to bet you it broke off as one big piece and wedged itself against the O2 sensor. It would technically be functioning properly since there is nothing mechanical to it and it is just metal that needs to heat up.

VasMan

FYG My check engine light did not come up till the next day.

VasMan

After reviewing the video, the cat seems to have broken at 4:12. Mine happened on a high rpm shift just like yours, when the traction control or stability system took over. Mine was bad enough that actually gave me an error for traction control. The error cleared as soon as I turned off the engine. I drove the car one more session and then I could hear a rattle from the cat.

If I were you I would not drive the car hard before I get to the bottom of this. Of course I would not go to the dealer with the video and ask them what they think... but keep your eyes and ears open the next few days.

When they replaced my cat, the Oxygen sensor crapped out too the next day, so make sure they check that if you indeed find out that this is a problem. It may save you a trip... Also ask them to check for lose pieces in the piping and mufflers.... they did not check mine and I had to go fish them out myself...