Boost Leak

I finally got around to building an Intake Pressure Tester, and tested my intake for leaks. My suspicions were confirm. I have a boost leak coming from the throttle body / EGR valve area. It has a very audible leak and looses about 1-2 psi per second. I could not pinpoint the source of the leak, though. All I know is that it's down in behind the throttle body next to the firewall. I tried using soapy water and looking for bubbles, but could not find it. It's very tight in that area on a 2G. You can't even get your hand down there.

Does anyone know what typically leaks down in that area?
Is a boost leak of 1-2 psi per second worth worrying about?

Probably throttle body shaft seals or some other small thing. What Psi do they start to leak at?
Ideally you want to get rid of all your boost leaks, but it seems anytime you fix one you notice two more another 5 psi higher. I'm hoping the injector o-rings and throttle body shaft seals are the only ones I have left, I'm sealed everything else

It starts to leak as low as 5 psi, and leaks all the way down to 0 psi at a rate of approximately 1-2 psi / second.

I'd consider that a bad leak then. I don't start to lose any air until around 18psi, but I've replaced gaskets and used RTv on almost everything in the intake system

That's what I was afraid of... So what do people typically do for hard-to-pinpoint leaks such as this? Start tearing apart the intake, replacing gaskets and such? Any tips for a boost-leak newbie? :-)

Being a 2G, I guess your car isn't that old. Has it ever been to the mechanic? Sometimes parts come off and go back on without the necessary gaskets getting replaced. So maybe you need to replace the intake manifold gasket, and those 2 TB gaskets. Just a thought...

I'd say replace your two TB gaskets first, check and make sure all your hose clamps are tight and your BOV flange and BOV aren't leaking (you might want to link to a webpage with your list of mods) if you get most of the big spots done you sohuld be able to hold 18 psi or so without issue, the little problems like TB shaft seals and injector o-rings aren't as severe.

Sounds like the throttle body shaft seals... do a search in the archives.

I don't believe the intake has ever been disassembled, but I can't say for sure as I bought the car used. I don't see any evidence in the service records though.




The boost leak is very audible and I have no doubt that it's coming from the throttle body / EGR valve area. I may have other leaks, but this one is by far the worst and drowns out any other audible leaks.




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Thanks guys. I appreciate your help.

Maybe this is why you didn't notice a difference when you upgraded your BOV and UIP.... Like the other guys said I would check the TB shaft seals and the TB gasket before I went anywhere else.... you kinda have to do this in the order of the biggest leak first.... and I would say that if it starts leaking @ 5psi and bleeds down fast.... then that is a big leak.
A.

After some subsequent intake pressure testing, I discovered my boost leak is originating from around the throttle body shaft area...

This lead me to believe the problem is my throttle body shaft seals. So I called up my local dealership to order a new set, but they don't even list these seals.

Has anyone ever replaced these seals with new OEM replacements? If so, do you have a part number? I missed out on Andrew Bienhaus' group buy back in December.

Thanks.

I was looking into this last year, the dealer doesn't sell just the seals, you have to buy the whole throttle body. I was going to look for some seals this spring but then Andrew came out with the group buy. They are a special o-ring with a metal center, you can't just throw in any ordinary c-ring.

As the car sits I can't get the system to hold any pressure. Pumping in 30+ psi, the gauge would only go to 5psi and as soon as you take away the air it doesn't hold anything. When you have such a boost leek your turbo has to work extra hard to build and maintain boost....but I was still able to manage a 13.2@105 with these leeks.

[ February 26, 2002: Message edited by: Vince Amato ]