[s-cars] Boost leak help!

[Daniel Hussey]

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Ok, I'm having some trouble with a boost or vaccum system leak and can't se=
em to find the source.

Here's the rundown...  car is a 1995 Audi S6 Avant.  Never had any problems=
, car ran great, but started noticing loss of some boost power after instal=
ling a TAP 2.5 bar chipset and AutoMeter boost guage.  Car was only pulling=
 10 psi, then it petered out and you heard rushing air.  Otherwise, the car=
 drove fine and under normal conditions you would not notice any problems. =
 So, I figured I had a split in my lower boost hoses somewhere.  So, I orde=
red a Samco Michelin man hose (everyone was out of stock on the turbo to cr=
oss-over pipe one at the time).

Anyways, without replacing any hoses (while waiting for my Samco to arrive)=
, the problem seemed to go away!  I was pulling 15-16 lbs of boost normally=
 (which seemed about right for a 2.5 bar sensor car and stock position of t=
he wastegate spring).  No rushing air sound.  Car drove great.

Then, all of a sudden last week, the problem came back.  Same symptoms.  Ca=
r pulls a good 10 psi, then I hear air rushing out and that's as much boost=
 as it can pull.  So, I decided to actually replace my cross-over to IC hos=
e with the Samco unit.  Nope, problem still there.  I inspected all other b=
oost hoses carefully (including the one I pulled off when I replaced it).  =
All in great shape.

So, next step, I pressurized the entire intake system to 15-20 psi.  At abo=
ut 10 psi the only air I could hear rushing out was through the oil cap... =
 it was loud too!

Is this normal?  Should the oil cap let air pass through?  I've never heard=
 of this as a source of boost leaks, but I'm wondering if anyone else found=
 this to be a pressure leak causing low boost?

BTW, I have also replaced the bypass valve with an upgraded unit (993TT fac=
tory part), and replaced the lead hose with Gates fuel hose with good hose =
clamps, and car pulls no codes.

Any ideas???  Should I replace the oil cap?  And, if this is not my source =
of air leak, where else should I be looking?  I think I've been checking al=
l the obvious places.

Thanks,
Dan
'95 S6 Avant (factory "Sport" suspension)
'87 Jeep Cherokee 4x4 (aka "Ski Bitch")
Seattle, WA

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