[s-cars] Help with a "moisture trap" definition re: boost gaugeinstallation

[Dave Forgie]

Steve: Thanks very much for your thoughts and information.  It is curious that ETKA calls it a "fuel condensor" but the VW master price list calls it a "filter".  I contend that the only way to keep oil and water (or fuel or whatever) out of the ECU is that this $5 thingamajig (tm)  has an oil/fuel resistant membrane inside the two-nippled plastic "can".  I have ordered a new one and will be cutting it (or my old one) apart to prove/disprove my (and others) theories.

Thanks also for the pressure transducer and A/D info.  I am an environmental engineer who understands hydraulics not bad but electrical stuff is a bit "smoke and mirrors"  sometimes.

Dave F.

>>> Steve Eiche <seiche at shadetreesoftware.com> 5:42:09 PM 7/7/2003 >>>
Hmmm, so what's the issue?  You can get you signal for the gauge
anywhere that you like for the boost gauge.  Before the trap, after the
trap whatever.

The trap ("condensor" according to the Audi literature) is there to keep
oil and water out of the ECU.  Old Audis (5k and 5kts, especially) had
problems with getting oil int the A/C control system and to a lesser
extent the engine ECUs.  Anyone who owned an '84 to '88 5k, like myself,
likely experienced the exact problems remedied by the condensors when
their climate control system failed.

The element in the pressure sensor, which is basically an absolute
pressure to voltage converter (~0 to 2.5 bar = ~0-5V - depending upon
the sensor, be it stock 2.5 bar, 3 bar or whatever), does not like
having contaminents in it, which will damage or slow their response.
The trap is simply a filter to keep the sensor element clean and dry.

As for how the ECU "reads" the Manifold Absolute Pressure (MAP), MAP is
  expressed by a DC voltage from the absolute pressure sensor in the ECU
and read by a D/A converter which translates the analog voltage to a
digital value at a certain address that can be used by the boost control
program in the processor.

Just subtract "air/fuel mixture" from your statement and you are pretty
much correct.  There should be no fuel in the intake at the point at
which the pressure is sampled.

Steve

Gentlemen:  I have been having an internet "conversation" with an
"internationally reknowed" (in his opinion) "20vt tuner" (You can guess
who).  The point of the discussion is my understanding about the
"moisture trap" (which is isn't) and my contention that you should be
able to T a boost gauge anywhere downstream of the "trap".  What is
wrong with my statement below?  Comments and corrections appreciated.

Dave F. suggested:

"The 'moisture trap' (which is the wrong name for it) is an analogue to
analogue pressure  transducer, i.e. there is a air/fuel mixture pressure
"signal" from the intake manifold side of a  fuel resistant diaphram
which is translated to an air-only pressure "signal" in the plastic tube
leading to the ECU. The pressure transducer (2.5 BAR or 3 BAR) inside
the ECU box is analogue (pressure) to electrical and translates the
analogue pressure signal (can be read  on an analogue gauge) to a
millivolt electrical signal (that can be read with a multimeter - as you
well know) that is read by the chips in the ECU. (The one thing I don't
know is whether  the ECU pressure transducer also creates a digital
output from the millivolt pressure translation or there is something
else that does this before the chips).

In any event, to install an analogue pressure gauge, it should be fine
to T' off anywhere  downstream of the analogue pressure transducer and
before the ECU box. The advantage of  T-ing near the ECU is the analogue
pressure signal tube has already gone through the  firewall and into the
passenger cabin. "

  Dave F.