possible boost/vacuum leak... chime in

**obijohn22** · 08-04-2008 08:47 AM

Hey all,

did a boost leak test yesterday because i was concerned about a vacuum leak. I found a small leak and tightened a clamp but i have a few questions. this is the first time i have done this test.

1. I hear a small hiss coming from the throttle body area. to me it sounds like boost leaking by the throttle body. It is not leaking into the atmosphere that i can tell. Is this normal?
2. I removed the oil fill cap to prevent hissing from the crankase, and when i return it into place and plug the PCV valve with my thumb, after pressure builds a little i can start to hear a little hiss down by the front of the intake mani on the drivers side. this one concerns me a little. BTW, just did my afterrun pump and intake gaskets 3 weeks ago. But the boost and vacuum do not read any differently than they did before.

when i start the car cold, vacuum is at around 18 hg or so. if i raise the rpm to around 1000, still in park, i get 20 hg. coasting in gear i get 21 hg. after car is hot at idle in park i get around 16-17 hg.

What do you think? boost seems normal.

**RolledMySTi** · 08-04-2008 08:55 AM

You need to pressure test again. Fill a spray bottle with soaping water and start spraying parts when you pressure test. Where you see bubbles is where you have a problem.

**BITRBO** · 08-04-2008 09:58 AM

^2nd.

**AudiSportB5S4** · 08-04-2008 12:35 PM

3rd, usually your vacuum at startup is generally lower ( like you said you have 18 when cold then when warm its 16-17 ) it should be the other way around, but 16-17 is kindaaa low. Things like your air intake setup (stock airbox or not) can affect but as the others said check for leaks. even the Samco TBB can tear, and since you're a 2000 like me, check the F hose. the F hose being torn for so long in my car led to the K03s poppin!

**obijohn22** · 08-04-2008 12:50 PM

good stuff guys i'll try all of that. I was under the impression that the pressure tester is only good for testing the system up until the throttle body. I am hearing this slight hiss near the intake manifold.

any ideas on this one and how to test? I will definately use the soapy water test. I was hoping somenone on here would have some experience with post throttle body leaks and how to track them down. prior to the throttle body, all is well. thank you for the replys and keep the ideas coming!

**AudiSportB5S4** · 08-04-2008 01:32 PM

ahh hiss near the intake mani?? are your injectors seated correctly?? have they ever been touched, if so they could not be seated all the way in, as if you should remove Y pipe and push down on them if you can OR your injector O rings, if they are really old and have never been touched can be leaking.... somehow you have to spray some water down there. i would take off Y pipe, spray each injector, attach Y pipe and look for bubbles....

**obijohn22** · 08-04-2008 04:47 PM

good points, i'll add them to the list.

thanks. anything else anyone can think of? I would like to get the best list of items to check together so i can be thorough the next time i raise the hood.

**AudiSportB5S4** · 08-04-2008 07:17 PM

i would REALLY think first start small at the F hose... since you're 00 like i am... one time coming home from the city i wasnt boosting quite as high as i used to (at the time i had GIAC and 19 was normal) so for a few days i thought i had a bad tank of gas possibly. i even made a youtube video LOL titled "GIAC X BAD GAS" after pressure testing, which many people seem eeh i dont NEED to, i found a leak at a few clamps. so i fix the leak and i still had air coming out... sure enough it was that dam little F hose, and during the install the clamp fell off, F hose came loose, and i sucked something in just eating the turbo to bits. so go out there and fix it! haha

**nvrfollow** · 08-04-2008 09:47 PM

A bolt on my drivers side turbo was backing out causing a major leak. Not sure how common that is?

Good luck finding your problem!

**eduard95670** · 01-22-2013 11:58 AM

Some aviation mechanics recommended to spray brake cleaner and listen to rpm rise, you found your leak.

**Luvshok** · 01-22-2013 12:10 PM

Originally Posted by nvrfollow

A bolt on my drivers side turbo was backing out causing a major leak. Not sure how common that is?

Good luck finding your problem!

I have a boost leak coming from my drivers side turbo, and this may be my issue. It's been a bit cold the past few days to be in the garage so I haven't gotten a chance to get back under the car.

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**s4Bman** · 07-31-2016 08:40 PM

So what all did u have to do to get the passenger wastegate line fixed?

**01audia4** · 07-31-2016 08:58 PM

Originally Posted by s4Bman

So what all did u have to do to get the passenger wastegate line fixed?

Replace it.

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**getslideways** · 07-31-2016 11:43 PM

Originally Posted by s4Bman

So what all did u have to do to get the passenger wastegate line fixed?

I don't see anyone in this 2 year old thread mention a wastegate

**Zba** · 08-01-2016 06:23 AM

Originally Posted by getslideways

I don't see anyone in this 2 year old thread mention a wastegate

Eight years old. This thread is eight, years, old.

**getslideways** · 08-03-2016 12:15 PM

Originally Posted by Zba

Eight years old. This thread is eight, years, old.

holy moley, i just read the '13 date on the last few posts and thought that was bad, didn't realize the thread had been borrowed from The Smithsonian!