[s-cars] still looking for missing boost

[Theodore Chen]

thanks for the tips, guys.

that's a quick and easy check.  i'll try that.
is it possible that the wastegate spring is failing?
i don't know if that'd cause the intermittent symptoms
that i've been seeing, though.

it occurred to me to disconnect the hose between the WGFV
and the wastegate, and _carefully_ bringing the boost up
to see if it consistently boosts to 2.1 bar (indicated on
the digital boost gauge, with 3 bar pressure transducer).

the other thing i'm considering is unplugging the connector
to the WGFV (thereby shutting it down) to see if i get
a consistent 1.2 bar reading.  there were a few times when
i saw less than that.  i figured that was just measurement
error, but it may indicate a torn WG diaphragm or worn spring.

-teddy

--- Kenneth Keith <auditude at gmail.com> wrote:

> Just put vacuum on the the nipple on the cap.  It should hold a vacuum
> unless it is torn.
> 
> Ken
> 
> "Mark Strangways" <Strangconst at rogers.com>
> >
> > Sounds like the WG diaphragm is ripped.
> >
> > Next move I would make is to visually inspect the wastegate.
> >
> > Mark
> > ----- Original Message -----
> > From: "Theodore Chen" <tedebearp at yahoo.com>
> >
> > > symptoms: inconsistent low boost.  sometimes i get full boost or
> > > close to it.  other times i get only a few psi (which i assume
> > > is due to the wastegate spring).   it is inconsistent and changes
> > > during the course of a drive.  it has occasionally even changed
> > > during the same acceleration run.  sometimes it feels like it's
> > > spooling slowly and then the boost suddenly comes on.
> > >
> > > things done so far:
> > > 1.  replaced all of the little boost hoses between intake,
> > > fuel pressure regulator, tee, moisture trap, and ECU.  used
> > > bicycle pump to verify that it would hold at least 20 psi, and
> > > a mityvac showed no leaks.
> > > 2.  all hoses in intake tract (turbo to XC, XC to IC, IC
> > > to TB) are samco with t-bolt clamps, and have been checked.
> > > 3.  bypass valve is a forge, and its operation has been
> > > verified with a mityvac.  i also tried to blow through it
> > > to confirm that it wasn't leaking.
> > > 4.  replaced little boost/vacuum hose from manifold to bypass
> > > valve.
> > > 5.  output tests run and WGFV (wastegate frequency valve)
> > > clicks.
> > > 6.  ECU checked with VAG-COM.  no codes except for engine
> > > position sensor (the engine wasn't running so it's ok).
> > > 7.  pressurized the hose from the WGFV to the WG to 20 psi
> > > with a bicycle pump.  it leaked down quickly to about 10 psi,
> > > held, and then suddenly leaked all the way down, with an
> > > audible sound from the wastegate.  this happened every time.
> > > i'm not sure if this is normal.  is it?
> > >
> > > can a WGFV pass the output test and still be bad?  is it
> > > possible for the WGFV to fail intermittently?  or work well
> > > enough to pass the output test but not cycle rapidly when
> > > commanded to do so by the ECU?
> > >
> > > i'm not sure what to try next.  i could replace the O2 sensor,
> > > since i'm not sure it has ever been replaced.  the car has
> > > nearly 132k miles now.
> > >
> > > by the way, i now have a hoppen-sourced silicone turbo to XC
> > > hose available if anybody needs to buy one.  perfect condition.
> > > i wasted time swapping it, but at least i eliminated one more
> > > possibility.
> > >
> > > -teddy
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