[s-cars] Pressure Test

[Bob Rossato]

I see a couple of issues here.

Since you mentioned that you were having your wife monitor pressure via your
boost gauge I'm assuming that you didn't disconnect and plug the hose at the
throttle body and ISV.  If not, you're only going to bleed the system down
unless you're lucky enough not to have a cylinder with the intake and
exhaust valves slightly open.  I believe there is always some overlap; the
intakes start to open before the exhaust valves fully close.   Unless I'm
missing something here, I believe the only way to properly do this test is
to remove the hose from the throttle body and ISV and plug both of those
openings.

If you did plug the hoses at the throttle valve and ISV, because you started
off with a finite volume and pressure in the tank, once you hooked it up and
equalized the system you will end up with a lower overall system pressure.
You have quite a lot of intake tract volume between the MAF and throttle
body, and since you only started with a 2 gallon reservoir your final
pressure would drop significantly.  Plus the gauges on those portable tanks
are notoriously inaccurate to begin with.

Bob

> -----Original Message-----
> From: s-car-list-admin at audifans.com
> [mailto:s-car-list-admin at audifans.com]On Behalf Of Ed Walsh
> Sent: Sunday, April 27, 2003 9:40 AM
> To: s-car-list at audifans.com
> Subject: [s-cars] Pressure Test
>
>
> Some may know, ad nauseum, that I have been trying to
> fix a lower than expected max boost issue.  S6 MTM 1+.
>  (stumble appears to have been fixed my BM's MAF)
>
> It was recommended that I try to pressure test the
> motor to see if I have any leaks (minor ones that
> would appear only under boost).  Well, after testing,
> I think I might....
>
> I made an adapter out of a 3" male sewer clean-out cap
> (great tip!), for the hose that attaches to the MAF.
> I installed an air compressor quick connect adapter
> thru the cap.  All is air tight.  Here is what I did
> the perform the test, tell me if I am doing this
> righto:
>
> - Told wife she looked nice today and that I was
> looking forward to her parents next visit
> - Pressurized my 2 gallon portable air tank to ~20 PSI
> - Ask wife to help me read the boost gauge in my car
> :)
> - With wife/eyes in place, Connect quick connect to
> home brew adapter, pressurizing the system.
>
> My suspicion is/was that an air tight system would
> hold these 20 PSI and that it would indicate this on
> the boost gauge.  No?
>
> - Wife reports that, not only is it cold and boring in
> the garage, she only saw 2.5 PSI after I pressurized
> the system.  After about 10 seconds, the pressure on
> the gauge actually rose to about 3.5 PSI.  Weird?
> I'll explain.
>
> - When I initially connected the air tank to the
> adapter/cap, I heard a deep rush of air being moved.
> (like a jet engine heard from 30,000 ft below). I had
> thought this was just the system being pressurized,
> but it appears that the noise was from a leak.
> Where?, I don't know, but the sound seemed localized
> in the under the turbo area (crossover pipe?)
>
> I couldn't feel or see any air leaking, but it had to
> go somewhere... Or am I screwing the test up?
>
> I hypothesize that the reason the pressure actually
> rose to 3.5 PSI after about 10 seconds
> (coincidentally, the same amount of time I heard a
> deep rush of air being moved) was the result of the
> leak re sealing itself.  It would then hold that 3.5
> PSI for 30+ minutes.
>
> So, as long as I have done the test right, I may have
> figured this out.  Can anyone confirm the test is
> accurate b4 I battle hell's gate (the belly pan)?
>
> Thanks a Million,  Ed
>
>
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