Boost leak???

**xmoox** · 09-06-2008 09:34 PM

So today i was driving everything was fine hitting 15lbs of boost no problem then on my way back i was driving in 6th gear and then hit 15lbs and held steady and it kinda shuddered and i backed off. At first i thought it might be the clutch so then i tried 5th and hit 15lbs of boost then went down to 10 and still shuddered. when i was close to home i tried full boost in second gear and got to 15 then dropped down to 5lbs so is that a boost leak or something else. im going to try to build a system to pressurize my engine with a bike pump. just a question is it going to screw up anything if i just drive it and not boost just try to keep the boost under 5 so i can still have a car until i can take it into a shop and have them look at it or do you think i could just boost test it myself. its a 2000 audi s4. And Im in the Portland area if anyone can help me out. its a great car i love it best car Ive ever owned. the cars hitting 20 vacuum and thats normal i think. its an epl tune if that helps.

**xmoox** · 09-06-2008 11:37 PM

well ive been reading could this be caused by a bad n75 valve and heres a good write up i found about pressure testing and some good info for anyone else having this problem

http://www.allroadfaq.com/downloads/...re_testing.pdf

and this helps
http://www.awe-tuning.com/media/pdf/...ure_tester.pdf

**VinNyS4** · 09-07-2008 10:10 AM

check the tbb

**bigbadboss101** · 09-07-2008 10:14 AM

Before disconnecting is there signs to tell if it's the clutch vs MAF or TBB or DV? If one does a leak test and don't find anything I guess it can still be the TBB or DV.

XMOOX sounds like is experience it at high speed/gear.

**xmoox** · 09-07-2008 10:59 AM

I will check the tbb and the diverter valves. i have forge 007s diverter valves and silicone tbb. i dont know yet how to check the diverter valves and i hear they need to be lubed so that may be the problem. Im also going to check the F hose cept i dont know were thats at going to check my bently manual.

**Mike@Forge** · 09-07-2008 11:32 AM

We do recommend that our valves are cleaned and re-greased periodically, but there is no specific interval that is required. Once a year or so is probably fine for most situations/conditions.

To check the valve to ensure that they hold pressure/vacuum sufficiently, push up on the piston with your finger or a pen and then put another finger over the vacuum nipple to create a seal. The piston should remain up only dropping down slightly because of the spring tension, but not completely coming back to its seat. It should abruptly close only once you remove your finger from the nipple.

If the piston remains up, it should be holding pressure/vacuum just fine.

If it comes all the way back to its seat before you take your finger off of the nipple, there is probably a small leak with one of the o-rings. Re-greasing the valve might fix it, otherwise we might need to send you new o-rings.

Also, based on the boost pressure that your application is making, you should either be using the Green colored spring with one or two shims, or possibly the Yellow colored spring.

http://forgemotorsport.com/content.a...roduct=FMDVTUN

**xmoox** · 09-07-2008 12:05 PM

okay i will check thanks for the quick response. another thing as ive been reading about other peoples boost leaks when this car was vag-comed it said my requested boost or computer read boost was like 18lbs and the boost gauge said 15. And if this is a worst case boost leak like one on the turbo outlet do i need to pull the whole engine to get to it. car has new turbos 4000 miles.

**xmoox** · 09-07-2008 03:42 PM

okay so i took it for a drive today and tried driving around it was actually going fine it would hold boost at 15 for a little bit but then the problem started again after about 20 min of driving. The previous owner said he had this problem and it turned out to be a bad injector in one of the cylinders so i might have another one going bad. Also when testing it again it would hold boost then drop down to 10psi then flashed the check engine light for about 10 seconds then went off. I think im going to bite the bullet and have it checked out at a mechanics. it runs fine until i hit 15lbs of boost then cuts out.(i guess it could be 15lbs is what it takes for the boost to leak out)