Fender0122

A little background on the car: It's a '97.5 with 263,xxx miles on it. It's chipped, running 16psi (yes, I know, stupid on a high mileage car but the car came that way and the thing is in great mechanical condition) and Forge Splitter DV. Started getting this noise from the turbo at ~250,xxx. It had a bit of a chatter in low rpm and became a squeal as boost exceeded 3psi. I first checked for boost leaks and fixed a couple, mainly being a broken check valve and weak worm clamp. Replaced every worm clamp just for safe measures. Nothing changed. Replaced the clutch in the meantime with an s4 clutch and LWFW thinking it was slipping causing the squeal. Also replaced the wastegate with another stock unit. There were no records of the turbo being replaced or rebuilt, so I just did a rebuild on it this past weekend. There was surprisingly little shaft play side-to-side and none in-and-out to begin with, but figured it was a safe bet the thing was tired. Inspected the turbo while it was apart and found some deep cracks in the exhaust housing, but everything looked really good for such a used turbo. No bent fins, no marks on the shaft, but I did notice a chunk of something in the way of the turbine fins (pictured below). I figured that was what the low rpm chatter and subsequent squealing was so I ground it off. I didn't have the money or resources to wait and get a different housing, so I put some manifold crack sealant in the cracks, hoped it wouldn't cause any problems, and put it all back together. I got the car running, took it out and found the chatter and loud squealing was gone, but a definite hiss is still there. Checked again for leaks by plugging off the charge piping from the turbo to throttle body. Everything good there. Reconnected the pipe to the TB and tested it again to see if I had leaks in the intake mani or vacuum lines. Everything seems good there. I am now baffled on what the squealing is. Could it still be the cracks in the housing? Gutted cat causing a whistle? I also have replaced the flex pipe with a generic one from Advance Auto, could that cause the whistle? What about the N75 valve?

Thanks for any help!

Here are pics of the cracks, chunk on the housing (before I ground it off), and a video of the whistle I'm talking about. You can kinda hear how the boost varies when it finally hits 16psi in 3rd gear, which makes me think a boost leak (or N75 valve?).





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turbo510

Exhaust leak? My Passat's turbine housing flange was not all that flat, so I filed it.

Fender0122

I cleaned up the flanges with a file, too, and put on new gaskets, so I dont think thats the problem. I almost thinking it's that darn flex pipe, since it's actually making up part of the bend as the pipe goes towards the bottom of the car.

audinutt

The crack in the housing is BAD news, you need to replace the turbo, it will only get worse in time, mine did the same thing at about 200K miles.

This is the hissing you are hearing.

Fender0122

Well that's exactly what I was thinking, so I went and bought a k04. I also replaced the manifold since it had slight cracks in it, but that didn't help at all. I swapped out N75's with my buddy's car and nothing changed either. I have started chasing vacuum lines and pressurizing them to test the one-way valves, no dice. Replaced the lines on the N75 and DV as well.

What's weird is that now my max boost fluctuates much more now, between 13-16psi. It hit 20psi at one point and held through the gear, but I've never hit that since. The car is chipped on some unknown tune, so I think that might cause the boost fluctuations, but still doesnt explain the squeal.

Fender0122

So I finally found the problem! It ended up being the stupid flex pipe. I decided to make my own 3" downpipe and replaced the flex with a shorter unit and it fixed the noise. The car sounds nasty now. I ended up putting the flex further down stream like 034's exhaust setup, mainly bc a 3" flex is twice the price and I was on a budget build and didn't plumb it all to 3" yet. When I do finish it all in 3", I'll buy a new flex and put it back in its stockish location.




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