There's a Banshee Under My Hood (or: Boost Leak?)

Hi all.

For some background, my Legacy has a Crucial catless uppipe, Crucial shorty (catless) downpipe, and an AP with Cobb's Stage 2 map.

 

Last week I had the clutch replaced. I went easy on the driving at first, but after a couple days I started hearing a screaming sound from the engine bay when getting into the boost. It's definitely boost-related, not RPM-related, and gradually gets louder as the pressure goes up.

 

I haven't run logs, but from what I could see from watching the real-time boost pressure with the AP, I was hitting about ~14psi (I think I normally would get to ~16-17) and the pressure seemed to fluctuate quite a bit. Out-of-boost driving didn't seem affected at all (i.e. I don't notice a rougher idle than usual or

 

Thinking it was probably due to something not being tightened properly after the clutch replacement, I checked everything I could in the engine bay. Throttle body hose from the TMIC seemed a little loose so I tightened it. Vacuum hoses coming off the BPV and on the infamous blue T-fitting underneath the TMIC were still attached. The TMIC-turbo connection seemed tight. I did notice that I had several bent tabs on the (stock) TMIC, however, and it looked like one of the end tanks was detaching from the intercooler. I tried pushing it back in and crimping the tabs with pliers, but it made no difference. I also tightened the throttle body hose, also with no result.

 

So, figuring that it may be the TMIC leaking, I replaced it today with an AVO TMIC. Unfortunately, I've still got the scream.

 

The sound is loud enough to hear with the windows closed and the A/C on, and even shows up at relatively low pressures (3-4psi). I think the car feels slower than normal. The sound is very hard to localize - only thing I can really tell is that it seems to be coming from the engine bay.

 

Does anybody have any ideas on what to check next? I know as part of the clutch replacement they took the shorty DP off, but I'm not sure if one of the gaskets on it would have this result (a leak from the DP shouldn't affect anything except the sound, right?). I don't know if the turbo was disconnected from the UP. I had used the Crucial copper gaskets when I installed the UP & DP; I've read some bad things about them recently.

 

Any suggestions would be appreciated!

Sounds like pre turbo boost leak

Sounds like an UP leak. Check those gaskets.

Sounds like pre turbo boost leak

 

 

Sounds like an UP leak. Check those gaskets.

Thanks everyone. Now to go through the pain of taking out the uppipe again.

Well I finally got to work on the leak. Got the uppipe and downpipe out, changed all the gaskets (the manifold to uppipe gasket was definitely blown). Got everything put back together tonight and went out for a drive........and there's still a leak! Only now instead of a banshee scream it's a higher-pitched whistle (almost like a high-pitched kazoo sound). I didn't get a chance to really see if it has any effect on the boost pressure.

 

Ugh, anyone want to buy a car with a boost leak?

Check the turbo inlet pipe

I had the same sound and it turned out to be the turbo/IC connection. Is the rubber donut gasket installed on that connection? There is a groove on the IC itself in which the gaskets fits into.

I had the same sound and it turned out to be the turbo/IC connection. Is the rubber donut gasket installed on that connection? There is a groove on the IC itself in which the gaskets fits into.

 

There's actually a gasket there that came with my AVO intercooler.

 

The threads on one side are stripped, though, so I wasn't able to tighten it down as well as I should have. That's my prime suspect now.

There's actually a gasket there that came with my AVO intercooler.

 

The threads on one side are stripped, though, so I wasn't able to tighten it down as well as I should have. That's my prime suspect now.

 

I took that bolt out and then retightened it as much as I could today (at a certain point of course it just spins and spins without ever getting really tight). Going for another short drive, the sound was gone except for at higher boost pressures, so hopefully that is where the leak is. Now I have to figure out a solution for the stripped threads problem.

I took that bolt out and then retightened it as much as I could today (at a certain point of course it just spins and spins without ever getting really tight). Going for another short drive, the sound was gone except for at higher boost pressures, so hopefully that is where the leak is. Now I have to figure out a solution for the stripped threads problem.

 

Yeah I ended up stripping out the holes in my turbo too. The torque on those bolts is only supposed to be 26ft-lbs because the turbo is soft aluminum. I fixed the threads using Helicoil inserts (this kit here: [ame=http://www.amazon.com/Helicoil-5546-8-Metric-Coarse-Thread/dp/B0002SREP4/ref=sr_1_2?ie=UTF8&s=automotive&qid=1241211167&sr=8-2]Amazon.com: Helicoil 5546-8 M8 x 1.25 Metric Coarse Thread Repair Kit: Automotive[/ame] and you'll need a tap and die handle and a 21/64" drill bit too). The threads are much stronger now so there's no worry about them stripping out again. If you want a temporary fix, you can always run a bolt with some washers down through the hole and put a nut on the other end. There's not a lot of room to get the nut on there, but it works in the short term.

OR you could d what I do, just buy a longer, smaller diameter bolt and a nut. Slide the smaller bolt through the hole(s) and tighten with the nut.. In other words, forego the stock threading all together and use a nut.

Much better description and pics here..

 

http://www.legacygt.com/forums/showthread.php?t=75715&highlight=stripped+Turbo

OR you could d what I do, just buy a longer, smaller diameter bolt and a nut. Slide the smaller bolt through the hole(s) and tighten with the nut.. In other words, forego the stock threading all together and use a nut.

 

That's what I did, at least as a temporary measure. Not easy to get to the bottom side to hold the nut in order to tighten (the stripped threads were on the intake manifold side) but I got it somehow. Noise seems to be gone now! I'll have to recheck it later of course.

 

For those, interested, this is what my Crucial copper header-to-uppipe gasket looked like after 10,000 miles (it's now replaced with an OEM gasket):

OEM gaskets

OEM gaskets

OEM gaskets

 

All the copper gaskets I had used originally are now replaced with OEM gaskets. None of the others were as bad as that header-to-uppipe gasket though.

Semi-thread jack but related to leaks.

 

I cannot find the exhaust leak in my car for the love of god. Two shops have looked at it and have reported no physical leak(s), however I hear it every time my car is warming up. I can also smell the exhaust leak with the windows down, I bet the RTS oil does not help because it has a distinct stink itself.

 

Anyone have ideas. I am pretty sure all of my gaskets are OEM.

 

Relevant Mods are HKS Uppipe and Cobb Catted DP

I know a few folks who have had this leak, turned out, in a 3 cases it was uppipe to manifold joint. all 3 corrected with 2 gaskets. No one wanted to start rotating turbo housing Just curious, all 3 were rigid( no flex joint) uppipes. Anyone know of leaks with flex type(turbo XS or Avo) pipes?

I've had trouble with the Helix flex uppipe in the past... It was with a gruppe-s header though.. It took a bit of work and I probably went through about 6 gaskets before I finally got it to seat right.. Be careful on how you torque your bolts down.. Try to do it as even as possible. It's a real pain in the ass... I would go with a flex pipe instead of a solid pipe.. Even the Sti uppipe has a flex joint