wtf is that noise? (now with more video)

[Castor Troy]

http://www.youtube.com/watch?v=0guupJMGXL0

Have you guys ever heard a PCV valve sound like that before? I'm not sure if it's the PCV valve or not. Coming from the back of the engine, only does it at idle/low load betwee 700 and 2000rpm.

Reason I think it's the PCV valve is because it looks like every other part of the pcv and vacuum system has been replaced recently...

[Audi4.2]

sounds like a jet turbine...... i dont know what it is i hope nothing to serious. Good luck

[OGBULLYLOCDAWG]

SAI (secondary air injection pump)?


http://www.youtube.com/watch?v=xksFU5TFVDo

[Castor Troy]

no. like i said, it's coming from the back of the engine, not from under airbox where the sai pump is located

[Danik675]

At the back of the engine.

[G Men 08]

sounds like a vacuum line i broken. I had a slight whistle (not that loud) on my C4, it was a cracked vacuum line.

[redneck truck]

Lot of vacuum lines at the back of the engine. Have you done any work on the car recently?

[Castor Troy]

no, i havent done anything back there. and it only happens when the car is warm.

[G Men 08]

Any vacuum lines that go to the SAI?

[brewmastr]

remove the oil cap and see if it goes away, i once had a ML63 at work that would make a high pitched noise like that, the crank breather was clogged and blowing pressure by the rear main seal making a whistling noise like that.

[Castor Troy]

Bump. The squealing appears to be coming from under the intake manifold. I am beginning to think my PCV valve is clogged, and the high amount of vacuum is sucking air in through a fitting under the intake manifold.

When I take off the horizontal line going into the PCV valve(comes from the valve cover i believe) the engine doesnt really idle any differently. When I pull the PCV valve off completely, there is a TON of vacuum coming from the vertical line(which I assume goes into the intake manifold), and the engine basically won't idle. When I put a plug in that PCV line going to the intake, the squeal comes back.

Should I be able to blow through the PCV valve one way or the other? Would that be the proper way to test it?

[Brian's A6]

I have the exact same problem with my A6. Started this morning pulling into work. I did not hear the whine until I was parked\idle. It has to be vaccum related as vac is at its strongest at low rpm idle.

I am on my way home in a few to dig into this a little deeper.

Also BTW is your A6 a 4.2L?

-Brian

[redneck truck]

I'm writing this post assuming that you are a 2.8L or 4.2L, not a 2.7T

Under the intake manifold there is a valley cover plate, the gasket of which acts as an oil separator for the CCV system. Attached to it are two hoses, one of which fits into the plate with an o-ring. I don't know if that part of the crankcase would be under vacuum or pressure.

You should also check your air cleaner elbow, as the suction jet pump pushes into a rubber fitting which could be cracked.

The hose for the EVAP purge line is right there on top of the throttle body, and a leaking one of those would certainly make some noise, though you'd probably experience other symptoms as well.

Finally, I've heard people describe a failed CCV valve as making a sound similar to what you're experiencing. Does the CCV blow air out of the top? I don't believe it is supposed to.

I replaced my CCV, EVAP purge valve, suction jet pump, valley filler plate, and the two check valves underneath it that screw into the block. I re-sealed the valve covers and inspected all the rubber hoses and replaced the ones that looked questionable. Finally, I replaced the intake manifold and throttle body (sticking intake manifold rotary valves were causing weak midrange power), and the car runs better than it ever has. I know it's a lot of stuff to replace, but all of the above mentioned parts have rubber in them that breaks down when exposed to hydrocarbons, oil, water, air, time, etc. I've got a few of those bits laying around and would be happy to help you. If you need a known good intake manifold, throttle body, or suction jet pump, I've got one.

[Brian's A6]

Hey Redneck,

Thanks for the reply. I replaced the suction pump since I had it on the shelf to no avail. I replaced the CCV in the process of troubleshooting a mis-fire issue a couple of months ago, and it is still fine as when mine was blown, the car would shut off at stop lights. I will look into the valley plate when I have some time over the weekend. It is vaccum related because I can remove the oil filler cap or the oil dipstick to stop the whine. As far as affecting performance it is not. It still pulls like a freight train:)

Also, I am 4.2L

-Brian

[Castor Troy]

Figured i'd bump this thread. The noise persisted with the PCV valve removed and the line for the PCV valve blocked.

I dumped about half a bottle of Seafoam into the intake manifold through the PCV line. After that, no more noise...

[Brian's A6]

Figured i'd bump this thread. The noise persisted with the PCV valve removed and the line for the PCV valve blocked.

I dumped about half a bottle of Seafoam into the intake manifold through the PCV line. After that, no more noise...

Thanks for the update. Once the temperature dropped the noise went away so I stopped trying to locate the cause but has since came back. I will give that a try before removing the intake manifold.