By-pass valves

[Ben Swann]

No, just the opposite.  The Bypass valve is normally closed.  The control port is vacuum
actuated and tends to open the valve.  Positive manifold pressure will assist to force
or blow the valve open when vacuum is applied to the control port.  This happens only
when the throttle valve snaps shut while engine is under positive pressure - like
between shifts.

So the mityvac test is not necessarily going to tell you if the valve is opening
properly and some valves have beefier springs for higher boost pressure.

Also, if the valve is installed backwards then it may not open or flutter when opening,
or open when it should not open.  Funny thing is the way most valve are oriented, the
correct way does not look correct.  You  might want to verify that the direction of the
valve is correct.

See: http://www.gtquattro.com/Bypass-Valve.html that has a picture of how the valve is
connected/oriented.

Ben

[Date: Wed, 11 Aug 2010 17:56:43 -0400
From: Eric Sanborn <esanborn at gmail.com>
Subject: Re: By-pass valves
To: dgraber460 at aol.com
Cc: s-car-list at audifans.com, quattro at audifans.com
Message-ID:
	<AANLkTin-vkgjJaotOtbbX3ToE1Ab-yLvLzkJ2293n-xq at mail.gmail.com>
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I might be misunderstanding what you were testing, but they should only open
during boost.

On Aug 11, 2010 5:12 PM, <dgraber460 at aol.com> wrote:

List-et-al;
I have been chasing a full throttle issue on my 3B'd URQ for a few months
now. The symptoms have been a flattening and lack of power under full
throttle. My boost gauge has always shown full boost at 19-20, and it throws
no codes. I started to notice the moaning (not whooshing) noise when off
throttle, which I had heard before and found to be an aluminum bypass valve
that needed cleaning.
Since it had been running an OEM Bosch plastic valve, I pulled the Forge
valve off the S-Car and cleaned it up and installed it. On the drive this AM
it seems to have cured the issue. Time will tell if total cure.
The question I have is that I tried to test all 3 valves that I have while
messing around last night. I have 2 plastic, and 1 Forge valve. I hooked up
a vacuum pump that pulls 14 lb hg to each valve individually and _none_ of
them would pull open. Then I used my little Mighty Vac hand pump and the
Forge valve would pull open and stay. Neither plastic OEM valve would open
with either test. Does this indicate both OEMs are toast?
I assume the vacuum pump did not have a check valve and therefore could not
"build" vacuum as the Mighty Vac did, thus letting the valves flutter but
not pull open. Sound reasoning?
Also - is there a recommended lubricant that keeps the aluminum valves
happy, and functional, or should they remain dry?

Dennis
Denver
]