[s-cars] Chasing a boost leak

[Mike Claire]

Thanks Tom, that confirms what I thought from the diagrams I've seen from
Dave F. and others in various places.

The BPV seems to get held open at idle (or more accurately, when there's
sufficient vacuum).  It would seem that at WOT you'd lose vacuum and the BPV
would close.  So if a BPV is to blame for lost boost, it would have to be
because it can't hold pressure.  I'm no expert, I'm just spending way too
much time thinking about this stuff :)

Either way, at idle there's enough vacuum to easily hold the BPV wide open.
The spring is stiff and everything seems intact, so I have to assume it will
hold boost.  It's the 710N version.

Far as the oil cap, I didn't notice slight vacuum sucking it into place at
idle, but maybe.  The idle didn't stumble either.  I did notice that when I
gave it a little gas that it stayed put - it didn't jump off the valve
cover.  So no blow-by - at least I got that going for me.



Mike

On 4/15/07, Tom Green <trgreen at comcast.net> wrote:
>
> The valve cover should be under a slight vacuum, Mike, courtesy of the
> emissions system plumbing under the intake manifold that removes the
> products of piston blow-by and valve seal leaks and re-routes them
> back to the intake.  That hose actually runs through the valve cover
> from
> the crankcase, and the oil and fumes get sucked right into the
> turbocharger
> compressor and right back to the intake, except for the oil that
> collects in the
> MM hose and intercooler.
>
> If your system can't hold a vacuum, it may not operate the wastegate
> or the
> BPV properly to obtain full boost.  The WGFV and BPV require vacuum to
> operate properly, so just the electrical solenoid clicking is not
> good enough.
>
> A new oil cap gasket certainly can't hurt, but it still won't hold
> boost.  :-)  If your
> valve cover did get pressurized to 22psi with the engine running, I
> would
> expect the oil seals (and cap) to whistle an angry tune.  You should
> feel a
> slight resistance from the vacuum when removing the cap at idle and a
> slight stumble in engine rpm.
>
> Tom
>
>     -----Original message-----
> > Date: Sun, 15 Apr 2007 19:36:52 -0400
> > From: "Mike Claire" <mike.claire at gmail.com>
> > Subject: Re: [s-cars] Chasing a boost leak -
> > To: " Vincent Fr?geac " <s.sikss at gmail.com>
> > Cc: S-car list <s-car-list at audifans.com>
> > Message-ID:
> >       <d219f42d0704151636t5f7b4ed5qbe6ffd32ac4fd473 at mail.gmail.com>
> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> >
> > I hope you're right, I'd be catching a break if just changing the
> > oil cap
> > would fix it.  Does the valve cover actually build pressure to 22
> > lbs (in my
> > case, with a 1+ chip)?  I thought pressure would just leave via the
> > rubber
> > hose that connects to the intake bellows, on the engine side of the
> > MAF.
> > That wouldn't hold pressure, it goes straight back to the air filter.
> >
> >
> >
> > Mike
> >
> > On 4/15/07, Vincent Fr?geac <s.sikss at gmail.com> wrote:
> >>
> >> Mike,
> >>
> >> I think you found the culprit: valve cover oil cap. Mine was the
> >> crankshaft
> >> breather hose rubber elbow at the back of valve cover, or should I
> >> say the
> >> first leak was... Now it's leaking at the spark plug #3 valve cover
> >> gasket... until I repair it and boost find another place to leak.
> >>
> >>
> >>
> >> Vincent
>
>
>