[s-cars] While we are on the subject of WGFVs...

[Theodore Chen]

--- Robert Myers <bob at chips-ur-s.com> wrote:

> 
> Hi Y'all,
> 
> Elijah asks about a _clicking_ WGFV.  I'd like to ask about a 
> _sticking_ WGFV.  What symptoms would a failed WGFV produce if the 
> valve were to stick open?  How about closed?  Anyone ever observe this?

i want to know more about the WGFV as well.  i just asked 
about whether a WGFV that passes the output test can still 
be bad.

bob, if the WGFV were to stick open, you'd be getting
max boost all the time, until the flow restriction through
the WGFV's tube to the intake hose became high enough to
increase pressure sufficiently to open the wastegate.

if the WGFV stays closed, then you're going to get whatever
default boost you get from the wastegate spring, which is
about 6 psi.

i believe my intermittent low boost problems may be the
result of a failing WGFV.  it's passing the output test,
but i don't know whether it'll still function properly
when it's hot and asked to operate at a much higher duty
cycle.  the output test just actuates the WGFV once per 
second (or therebouts), and i'm sure that's much slower than
the ECU wants during high boost.

somebody on audiworld said he had sporadic failure of the
WGFV.  that could well be my problem.  best price i've 
found for a WGFV so far is $56.  not a huge amount of 
money, but i'd like to not throw money at the car replacing
parts unless i think they'll fix the problem.

i am thinking about first unplugging the WGFV to see what
default boost i get, and about disconnecting the wastegate
from the WGFV to see if the car is able to achieve high
boost.  i realize that the latter choice is dangerous because
there is no ability to dial out boost.

it would be nice to find out what signal is being sent
to the WGFV.  is the ECU calling for a higher duty cycle
and not getting it from the WGFV, or is the ECU not asking
for the higher duty cycle (in which case i need to look at
sensors)?  but i don't know how to check this with the car
in operation.  i need a portable oscilloscope, back probes,
and long wires.

it also occurred to me that the biturbo S4 has a WGFV that
i could borrow to test on the UrS4.  however, i'm not sure
it's prudent to attack a perfectly well-running audi for
parts, even temporarily.  better to let sleeping dogs lie?

-teddy


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