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2011 audi s5 100k miles A/t
Hey guys just recently picked up my s5 a week two or ago need recently deleted muffler for more sound added quad Y tip. Sound is only coming from one side is this from the exhaust being installed/welded incorrectly or due to the tip itself? Or perhaps there's an underlying issue. Car was routinely serviced by an Audi dealership and prev owner got a Carb cleaning every 30k miles. Total of 3 carbons cleans ...thanks for any help. I do have a set of spark plugs/oil change i will be doing later. I noticed when i changed the air intake filter it quieted down a tad.

Sound comes from only 1 side driver exhaust and makes a consistent flutter sound/shuffling. Its not a rattle so i suspect cats may be good?
 

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By flutter do you mean like a Ppfffp noise, sorry that's the best I can do with my keyboard.

I think it sounds like an exhaust leak, on a clamped joint or weld?

With a friend and engine running try and block the tail pipes with your hands, make sure they're not hot! as this will accentuate the noise if it is a leak.
 

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2007 S5 4.2 V8 Manual
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This is my S5 4.2 V8.
cant put my finger on why it sound different from one side to the other but i also have a misfire between 2000rpm and 3000rpm and not sure if both are related.
 

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I would say they are related and that pfft noise is the miss fire. The issue is on the right bank (stood looking at the engine).

Try pulling some coils if you don't have VCDS/VAGcom to tell you where the missfire is coming from. Unplug the coils one at a time, it should make the missfire worse, or if no different on that coil, then that is the cylinder with either dodgy coil or plug. It is quite difficult as the coil packs are plugged into an electrical rail, so can't simply unplug one at a time as they all unplug at the same time. You'll know what I mean when you look at it. Or just change the plugs and coils as you have the parts anyway.

When were the plugs last changed? have you ran a diagnostic check? This does need fixing and I wouldn't drive it much as the missfire can lead to cat failure.
 

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2007 S5 4.2 V8 Manual
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The plugs and coils have been changed and the misfire is still there. No misfire at idle, only misfires when going through 2000 rpm up to 3000 rpm slowly. And nothing showing on VCDS.
 

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Hmmm, strange! You say it doesn't missfire on idle, but that pffst noise is there on idle. Difficult to diagnose online. Can you do a video with someone giving it a little rev? It could be something in the exhaust giving the noise via gas blow by. You can get this with exhaust vales when they're not closed properly. But if you have simply had the back boxes deleted and a straight pipe put in with Y piece tail pipes, it would be an odd one if there is something blocking it inside!? If you hold your hand very close to the tail pipes does the exhaust gas feel the same on both sides? Might be difficult to tell on idle, so some revs might make it more obvious if there is a blockage.

Could you film underneath the offending side so I can see and hear where what would the location of the back boxes.

Even though it's had a carbon clean, you could still get a sticky valve or 2 which can give missfire symptoms.

Also the high pressure fuel pumps on these can give irregular running and issues.

Whereabouts are you?
 
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