[s-cars] Chasing a boost leak -

[Theodore Chen]

--- Mike Claire <mike.claire at gmail.com> wrote:

> re: the WGFV - I ran the Motronic diags described on Scott Mockrey's site,
> which includes the WGFV.  I'm talking about the test that checks the
> throttle pot, the injectors, the carbon canister valve, ISV, etc.  The WGFV
> clicks the same as it always has.  Is that good enough to eliminate it as a
> suspect?

hell, no.

i posted about this previously in my search for missing boost (i was
often getting only WG spring pressure).  my WGFV passed the output test 
easily.  i replaced all the little hoses for the boost control system.
when i disconnected the wastegate, i got full boost.  i kept coming back
to the WGFV as the culprit, but it passed the output test twice.  finally,
i ran out of practical alternatives, and decided to just replace the WGFV.
that solved the problem.  later, i had a chance to test the WGFV on a 
function generator, and from the sound, it was apparent that it was failing 
at higher duty cycles.

> I have Samcos with breeze clamps.  The entire intake system including PVC
> system pretty much holds 10 or 15 lbs pressure (using a 3 inch PVC pipe
> cleanout with a compressor quick connect tapped into it.  It doesn't hold
> pressure indefinately, it does leak down very slowly.   Mostly through the
> valve cover oil cap.  I had to push down pretty hard on it to build
> pressure.

i didn't do this.  once i found i was getting full boost with the wastegate
disconnected, i ruled out a boost leak in the intake system.

> Bob Myers reminded me to check the ECU connection in the cabin - good call
> because somehow I overlooked it.

get a mityvac, and apply it to one of the boost control hoses.  if the 
system holds vacuum, that isn't your problem.  no need to chase all the
connections.  i wish i had figured that out before i replaced all the hoses.
i was double-checking everything after the WGFV passed the output test, and
went out and bought a mityvac to assure myself that there weren't any leaks.

on the bright side, all the little hoses are fresh and good for another
100k+ miles.

you need to reduce the search space.  disconnect the WGFV and see how much
boost you get.  if you get full boost, you can start looking for boost
control issues.  first thing i'd do is run the output test, but that doesn't
rule out a faulty WGFV in my experience.  assuming everything passes, next
thing i'd do is test the boost control hoses with a mityvac.  the next step
would be to check the duty cycle of the signal sent to the WGFV by the ECU.
i have a multimeter that checks duty cycle, but i was lazy.  i decided to
bet on the WGFV since the ECU wasn't throwing any codes, and that turned out
to be the problem.

-teddy


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