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Old 02-05-2013, 09:58 PM   #1
sswiss3000
 
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Convertible Exhaust Butterfly Valve - Service Bulletin

Convertible Exhaust Baffle - Bulletin

So I just came back from the dealership after dropping of my 2012 convertible 2SS (L99) for some warranty work as well as an issue I had with a squeaky noise coming from the back of the car.

Long story short they informed me that it was caused by a butterfly valve that was in the exhaust pipe right between the resonator and the muffler. This valve only exists on the L99s (possibly convertibles, not sure) in order to reduce exhaust noise during idle or low RPM operation (AFM). The service manager will give me the bulletin number tomorrow so that I can poste it. Basically it’s a valve that is held shut with a small spring and will only open during high exhaust flow situation. Thus the quick squeaky noise whenever I hit the gas

I was surprised to hear that the Automatic convertibles have such a valve installed, as I personally have never read or heard anything about it till now.
Has anyone ever removed this valve? Would be interested to hear the exhaust sound difference and how bad the AFM sound would be

update: My dealership told me that this noise is normal after all!! I have a hard time believing that


"The 2011 Camaro Convertible SS equipped with the 6.2L engine (RPO L99) and the 6-speed automatic transmission (RPO MX0) may have a metallic or spring-type rattle noise that is usually heard at idle when parked next to a wall or when pulling into or out of a garage.
The exhaust system for the 2011 model year has been revised to reduce exhaust noises heard during Active Fuel Management (AFM) mode. This revision includes a spring-loaded valve placed in the exhaust system before the muffler"
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Last edited by sswiss3000; 06-12-2013 at 11:10 PM.
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Old 02-05-2013, 10:05 PM   #2
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Some folks have opened the butterfly a full turn to disable it. Have been tempted to try it to see how I'd like the exhaust note, but my guess is that it would be a royal pain to reset the spring to undo the mod if I didn't.

Anyone have experience with resetting the spring?
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Old 02-05-2013, 10:21 PM   #3
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I sure did notice how quiet my car was at idle, barely got a rumble at start up.
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Old 02-05-2013, 10:28 PM   #4
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I think it also has to do with reducing resonations when the AFM kicks in.... I used to hear the valve cycle when it would transfer back and fourth from V8 to V4 mode. Anyone who has changed out the exhaust (cat back) has removed these valves.
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Old 02-05-2013, 11:31 PM   #5
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I took mine in for this well over a year ago. Chevy dealership gave me a copy of the TSB and it says "no fix" for the problem.

I wasn't too worried about it since I was changing my exhaust anyway.
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Old 02-06-2013, 10:40 AM   #6
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Muffler delete will fix that problem real quick... cutting just in front of that butterfly.
One of the cheapest bang for your buck mods you can do.
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Old 02-06-2013, 10:47 AM   #7
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I thought those butterfly valves were on all L99's regardless if they were coupes or Verts.
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Old 02-06-2013, 10:49 AM   #8
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Is this an L99 thing only?
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Old 02-06-2013, 11:24 AM   #9
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Are you sure these are exclusive to the convertibles? I swapped out a cat-back system for a friend with an L99 coupe about a year ago, and could swear it had the valves as well. I was concerned at the time what impact it may have on the AFM, since I figured that was its purpose. She's never had an issue since removing it.
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Old 02-06-2013, 11:32 AM   #10
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Dealer put O -rings on mine - I wired mine open and started it could not tell any difference so took the wires off but did not drive it with them wired open
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Old 02-07-2013, 11:02 PM   #11
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It's definitely exclusive to the L99 verts. My 2010 L99 coupe did not have these but my 2011 L99 vert did (until I removed them :-). Local dealer also confirmed the butterflies are on the L99 verts only.
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Old 02-07-2013, 11:53 PM   #12
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Used a pliers to move the spring to hold the valve always open rather than always closed- I believe I moved it 4 positions. Gives it a little more popping! Also eliminated the slapping sound from the valve springing closed when revving the engine.
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Old 04-03-2013, 11:48 AM   #13
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Here's the info as written by GM for the 2011's. I was given a copy of it when I took my 2012 in for the same issue, but can't seem to find it now.

Here's a link to the service bulletin issue I was able to find on the web. And yes, acocrding to the document it is ONLY on the convertibles.

http://www.archivedsites.com/techlin...tle-noise.html

Text from article:
Exhaust Rattle Noise

By Blog Post on June 1, 2011 9:59 PM | No Comments

The 2011 Camaro Convertible SS equipped with the 6.2L engine (RPO L99) and the 6-speed automatic transmission (RPO MX0) may have a metallic or spring-type rattle noise that is usually heard at idle when parked next to a wall or when pulling into or out of a garage.


The exhaust system for the 2011 model year has been revised to reduce exhaust noises heard during Active Fuel Management (AFM) mode. This revision includes a spring-loaded valve placed in the exhaust system before the muffler. (Fig. 15)



t is characteristic of this spring-loaded valve to make some noise during engine operation or when tapping on the exhaust pipes. No parts should be replaced or repaired for this noise.

photo from article
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Old 04-15-2013, 01:24 AM   #14
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Do you guys also get a short squeak right before the exhaust butterfly valves pop open? its super annoying on mine, but the dealer is telling me that this is normal.
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Old 04-15-2013, 02:34 PM   #15
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I was annoyed at the random, but constant, tapping noise at idle coming from the rear.
The first time I heard it was sitting idling in my driveway.
I thought someone was having roof-work done next door...but it was Midnight.

I don't know what the second owner ever did.
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Old 04-17-2013, 01:22 PM   #16
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get some headers and exhaust....problem solved
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Old 04-17-2013, 11:40 PM   #17
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I just spot-welded mine open (after muffler delete), Much better full range sound at idle.
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Old 04-17-2013, 11:55 PM   #18
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Quote:
Originally Posted by steveintulsa View Post
I just spot-welded mine open (after muffler delete), Much better full range sound at idle.
Right on!
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Old 05-30-2013, 12:28 PM   #19
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I believe I have experienced this problem. I brought mine to the dealer and they told me there was a programming update that they did. Service guy said that it may or may not resolve the problem entirely, and that if it didn't, there was no fix for it. It seems to have fixed the problem as of right now, but not sure if it's a permanent fix. Glad to have found this information though.
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Old 05-30-2013, 12:57 PM   #20
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This is for the L99 only. My LS3 vert does not have these.
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Old 06-11-2013, 10:42 PM   #21
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I have new borla ateck all the way back. New borla headers and tune. What a differance in sound. They know your coming but very quite on the expressway.

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Old 06-12-2013, 04:24 AM   #22
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Would the Range AFM disable unit help keep the butterfly valves open all the time? If not, what is the best way to keep them open without putting in a new exhaust system? Any disadvantages to getting rid of the valves or having them permanetly open? Thanks in advance.
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Old 06-12-2013, 02:56 PM   #23
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Quote:
Originally Posted by SS PANTHER View Post
Would the Range AFM disable unit help keep the butterfly valves open all the time? If not, what is the best way to keep them open without putting in a new exhaust system? Any disadvantages to getting rid of the valves or having them permanetly open? Thanks in advance.
No, the exhaust baffles are not computer controlled or anything. Those butterfly valves are only opened when there is enough exhaust pressure (ie. RPMs).

On the other hand, you can either cut them out or simply wire them open if you have the Range AFM disabler installed, as they are designed to reduce the coffee grinder noise you get when the L99 engine goes into 4 cylinder mode.
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Old 06-12-2013, 02:59 PM   #24
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Quote:
Originally Posted by sswiss3000 View Post
No, the exhaust baffles are not computer controlled or anything. Those butterfly valves are only opened when there is enough exhaust pressure (ie. RPMs).

On the other hand, you can either cut them out or simply wire them open if you have the Range AFM disabler installed, as they are designed to reduce the coffee grinder noise you get when the L99 engine goes into 4 cylinder mode.
Thanks for the info.
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Old 06-12-2013, 06:20 PM   #25
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Quote:
Originally Posted by sswiss3000 View Post
No, the exhaust baffles are not computer controlled or anything. Those butterfly valves are only opened when there is enough exhaust pressure (ie. RPMs).

On the other hand, you can either cut them out or simply wire them open if you have the Range AFM disabler installed, as they are designed to reduce the coffee grinder noise you get when the L99 engine goes into 4 cylinder mode.

Explain "wire them open". I was going to find some to weld them open. If I can "wire them open" myself I would rather go that route first.
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