So sick of this woop woop noise - video....turn up your sound

[X-ZZ4]

Pretty much always does it at light to mid throttle going up a hill (under load). Sometimes it surges very lightly, sometimes worse. Not sure if the surge is related, probably. If I just keep the thottle in one spot, especially on a long hill, it will get worse. Give it more gas it will quiet down or go away. I've gone with different air intakes (including the stock air box), 3 different sets of diverters (2 piston type and tried different springs) and am now using the OEM plastic diaphragm type. Nothing seems to effect this. The sound is driving me nuts....sounds much worse in person. Don't know what it sounds like on the curb as I go by.....but it freaking embarrass me. It will do a very similar sound, louder, like loud chirp/bark, at the shift points at about 3/4 throttle, especially of I let off a bit at the shift.

This video is fairly minor, sometimes much worse.

https://www.youtube.com/watch?v=yJ8XPIycoGI


The car runs very well wide open throttle. Here's 20-95. Pulls good and smooth. And no barking/chirping/wooping. Just a smooth "swoosh" at the shift points like it shoiuld.

https://www.youtube.com/watch?v=Getp18mmPgo

But this mid-throttle/load thing is driving me nuts. I assume it has to be turbo related somehow, but I sure as hell can't pinpoint it.

[ImAudiHeree]

Sounds like pcv valve to me.

[X-ZZ4]

Sounds like pcv valve to me.

Interesting. Thanks. It's brand new....spider hose is brand new. Did it before I changed the spider as well. Honestly, I'm completely stumped. It just has to be vacuum or a boost leak I would think. Maybe I just need to get it in somewhere for a leak test and diagnosis. I just hate taking it in, especially with the mods and tune. Nobody I've already called seems eager to touch it.

Since you mention the pcv like maybe a breather issue......could it possibly be the oil cap? I've freaking replaced everything else. Guess that couldn't hurt.

[ImAudiHeree]

Yea that would be the best vacuum/boost leaks are tough to find. I just went in last week to a shop with my b6 s4 to try and find a vacuum leak I was chasing only charged me $80 for smoke test. Although I'm going to have to retest because I replaced every vacuum line on the front of the intake and it's still got shit idle, I can hear hissing somewhere drives me nuts.

[X-ZZ4]

Thanks. Yeah, my idle isn't exactly smooth either. I've suspected a vacuum leak somewhere for a while. I've replaced every suspect line....can't see anything else visually. I just ordered an oil cap from Amazon for the hell of it. I don't expect a solution but mine looks a bit beat anyway. And for $12 delivered to me.....what the hell, why not.

[JTown77]

Bub Rub is where i thought this was going/

[X-ZZ4]

Bub Rub is where i thought this was going/

I wish....LOL.

Didn't mention it above, no CEL, no codes.

[julex]

these are not stock turbos right? If they're not, then you simply have turbo surge which is normal once you install larger turbo and the're operating outside of their surge line like when you part throttle under load...

[X-ZZ4]

these are not stock turbos right? If they're not, then you simply have turbo surge which is normal once you install larger turbo and the're operating outside of their surge line like when you part throttle under load...

Yep, K04's.

One of my thoughts has also been wastegate flutter. Closest thing I can find to the sound while searching.

https://www.youtube.com/watch?v=oJgHdWle-Yk

But that seems more prevalent at blow off, not at medium acceleration, at least from what I can see. But hell, I don't know.

Hmmm.....got to about 1:50 of that video. That starts to sound similar. Thoughts? Is this what you mean by turbo surge?

[julex]

If it is a "chug, chug, chug" sound that goes away with slightly less or more gas pedal, then yes. It is the sound of compressor wheels stalling and then resuming operation. The turbo is basically outside of its surge line... now I would definitely boost pressure test the system to ensure that you don't have leaks that might make this much louder than it normally is.

[X-ZZ4]

If it is a "chug, chug, chug" sound that goes away with slightly less or more gas pedal, then yes. It is the sound of compressor wheels stalling and then resuming operation. The turbo is basically outside of its surge line... now I would definitely boost pressure test the system to ensure that you don't have leaks that might make this much louder than it normally is.

Thanks. Yeah....I think all roads lead down the boost/pressure test path.

But can you further explain the surge line? That's a term I'm not familiar with.

[julex]

http://www.turbosmartusa.com/technic...pressor-surge/

[X-ZZ4]

http://www.turbosmartusa.com/technic...pressor-surge/

Great little article....learned much in a few paragraphs....thanks!

Of course.....this leads me right back to diverters. The article talks about BOV's, but obviously we have diverters instead. And as I've mentioned, I've tried various combinations. While the combos I've tried have effected (positively and negatively) the power on the bottom end, none have done anything about the sound.

So are you saying just live with it? It's just a by-product of the K04's? That just doesn't seem right to me. My son has a friend with an S4 with K24's and he says it has no sound like this at all. He also says it flat out flies.

Of course, it's also a manual tranny....which seems A LOT more suited to these engines that the Tip auto. Really wish this car had one...power band is definitely much more stick friendly than auto.

Back to the article. Here's one of the last lines in it....

"What you want is somewhere between a ‘Pssh’ sounds and absolute silence. Anything else is slowly but surely costing you money and performance."

Well.....that's exactly what I have at full throttle and as shown by the second video in my first post. Damn....I'm so confused......

[julex]

It is possible that you might have a problem with N249, read about what it does here: http://www.audizine.com/forum/showth...ould-not-do-it


During part throttle, ECU is using vacuum from vacuum reservoir and N249 valve to open DVs even when there is near positive pressure in manifold, which normally wouldn't allow the DVs to open on their own. If your N249 is inoperational, then it is possible that it is causing the turbo stall since turbo has to work against a wall of air instead of having it freely circulate turbo-bipipes-DVs-turbo inlet pipes to prevent stall and increase engine efficiency.

[X-ZZ4]

It is possible that you might have a problem with N249, read about what it does here: http://www.audizine.com/forum/showth...ould-not-do-it


During part throttle, ECU is using vacuum from vacuum reservoir and N249 valve to open DVs even when there is near positive pressure in manifold, which normally wouldn't allow the DVs to open on their own. If your N249 is inoperational, then it is possible that it is causing the turbo stall since turbo has to work against a wall of air instead of having it freely circulate turbo-bipipes-DVs-turbo inlet pipes to prevent stall and increase engine efficiency.

Once again, you're a wealth of information. When julex speaks.....I listen. Thanks!

I had no idea about the N249. And this diagram from your link is extremely helpful.



Between the valve and the lines to the vacuum reservoir....I've got a whole new area to look at that I have not looked at before. This could very well be the source of a vacuum leak. I'll dig in as soon as I can, maybe over the weekend and report back.

Thanks again...you are extremely helpful and it is much appreciated.

[X-ZZ4]

Searching a bit more on the N249, I found this thread.

http://www.audizine.com/forum/showth...e-bypass/page1

I definitely need to take a look at the full line route and the reservoir, but what do you think about bypassing the valve? Seems to have been a fairly popular mod with some.

Hell who knows.....when I look I may find it's already been bypassed by the previous owner who did the whole K04 setup. Again....I'll report back.

[julex]

not a problem. With VCDS you can actually test the N249 while car is not running, you should hear clicking at it changes between internal routes for air. More advanced test would be disconnecting the lines t verify that it routes properly by simply blowing air in it while it is switching during the test.

It is also possible that while N249 might be ok, you might be losing vacuum due to faulty "Non-Return Valve" which is known to crack after so many year of heating cycles. Good test would be to simply start the car for few seconds to get vacuum into reservoir and then disconnect after about 30 secons after shutdown any of the hoses on the vacuum reservoir side of non-return valve. If you get good air suction into the hose, then you're good there. If not... you have your probable culprit.

[X-ZZ4]

I just went out and did a quick visual. Valve is definitely there and not bypassed, and looks OEM with the OEM style clamps still. That in itself is suspicious....a 15 year old untouched part. I then followed the vacuum line to the fenderwell and everything looked good there and the hard line is still in place. I guess I'll need to pull the wheel to follow it the rest of the way to the tank, and inspect the tank itself as well. This is all pretty suspicious. I know the car had been in a wreck and the driver front fender has bad been replaced before I bought it, so this whole area of the car is a bit suspect. It's not exactly a high quality repair either and obviously was done by the previous owner himself Although not horrible, definitely not a professional auto body quality repair.

And although the link above about the valve says it's easy to replace...not really. Still has the OEM clamps on it and with short little hoses. I'll have to redo all the hoses and clamps if I do indeed end up replacing the valve. Obviously not difficult, but not the 10 minute swap out some in that thread claim either. Regardless....I think I'm not on the right track here for the first time regarding this noise. Thanks again julex!

[X-ZZ4]

not a problem. With VCDS you can actually test the N249 while car is not running, you should hear clicking at it changes between internal routes for air. More advanced test would be disconnecting the lines t verify that it routes properly by simply blowing air in it while it is switching during the test.

It is also possible that while N249 might be ok, you might be losing vacuum due to faulty "Non-Return Valve" which is known to crack after so many year of heating cycles. Good test would be to simply start the car for few seconds to get vacuum into reservoir and then disconnect after about 30 secons after shutdown any of the hoses on the vacuum reservoir side of non-return valve. If you get good air suction into the hose, then you're good there. If not... you have your probable culprit.

Once again....great info. I'll do all this. Thanks again!

One point of related interest that may stir a thought to you.....

When the car is cold, especially at first start up in the morning, it has always (since I've owned it) had a low vacuum issue to the point the brakes barely work until it runs for 30 seconds or so. Other than the brake system/booster, does this point to anything possibly related to this?

[julex]

sounds like a leak in SAI/EGR to me. SAI valves are vacuum operated so if there is a large leak, that would affect the vacuum for booster. You really need to pressure test the engine to locate leaks.

[X-ZZ4]

Sounds like pcv valve to me.

Interesting. Thanks. It's brand new....spider hose is brand new. Did it before I changed the spider as well. Honestly, I'm completely stumped. It just has to be vacuum or a boost leak I would think. Maybe I just need to get it in somewhere for a leak test and diagnosis. I just hate taking it in, especially with the mods and tune. Nobody I've already called seems eager to touch it.

Since you mention the pcv like maybe a breather issue......could it possibly be the oil cap? I've freaking replaced everything else. Guess that couldn't hurt.

OH. MY. GOD.

The oil cap arrived from Amazon today. I popped it on and thought nothing more about it. Then later, I left to go to lunch with a friend, from which I just returned. Unbelievably, it made a HUGE difference. My idle is now completely smoothed out and the power on the low end is so much better and so much smoother. And also, what I mentioned about the brakes not working well when cold in one of my last post conversations with julex, well, that's gone now too. The vents on the cap were pretty crusty, and the gasket/seal on it looked questionable as well. But obviously, it had deteriated to the point it was effecting the way the car runs. It is unbelieveable to me what simply replacing the oil cap would do. I had no idea this could possibly do what it did. My woop-woop it still there.....but VERY minor now compared to how it was. Simply speaking, the car drives like a dream now.

I still can't believe it. I'm really waiting for next time I drive it for it not to be like this state of happiness....to revert back to unpleasantness. This has got to be the biggest surprise, and a very pleasant one I've had with this car yet. A $10 oil cap seems to have been one of my problems all along. I seriously would not have thought it possible. Thanks to ImAudiHeree for suggesting the PCV...that's what led me to think, "why not" and replace the cap. Simply unbelievable. I don't know whether to laugh now with excitement.....or cry uncontrollably because this has been at least one cause of my problems all along.

Still thanks to julex to his words of advice as well. I still have, but to a much lesser degree, a little of that woop woop sound and I'll continue to troubleshoot that.....but it is not nearly as bad and the car now drives so much better.

This car is freaking crazy. I've been around cars and worked on cars (mostly GM performance cars) for over 30 years.....and I have never, ever, seen an oil cap cause issues like this. Freaking unbelievable.

[X-ZZ4]

Old and new pics....

[ImAudiHeree]

Congrats I'm glad you were able to get that sorted out sometimes it's the most obvious things that stump ya!

[julex]

Congrats! Sounds like the cap was simply leaky and was introducing unmetered air into the system at idle when crankcase is in vacuum. Perhaps it was directly a source of sound (or its seal rather) when crankcase was at slight pressure, kind of like flailing piece of plastic can make awfully lots of sounds when deployed with wind present.