CIS Diagnostic, help

[rob hod]

    Steve,

    Looks like your testing at the right point, probably a silly question
but do you have the meter connected with the isolator tap on the right
side?, - tap towards fuel dist side?, If so then tap open = control pressure
reading, tap closed (engine off , fpr jumpered ) = fuel system pressure.

    BTW the bit you are requoting says "They could have used a spring, but
using fuel pressure
> > instead of a spring helps to compensate for minor fuel pressure
differences,
> > and saves needing another calibrated spring."

   Don't like to nitpick but this is wrong, - Control pressure, not system
pressure, is used to oppose the air flaps' movement, and the reason is that
control pressure, being regulated by the warm-up reg and any altitude
correction, determines the basic mixture (further modified by oxs/dpr in
emission control cars).

    HTH.

rob
>
> Message: 7
> Date: Mon, 06 May 2002 20:40:49 -0600
> From: Steve Sherman <spsherm at attglobal.net>
> Reply-To: spsherm at attglobal.net
> To: Bernard Littau <bernardl at acumenassociates.com>
> Cc: quattro <quattro at audifans.com>,
> Ben Swann <bswann at worldnet.att.net>
> Subject: Re: CIS Diagnostic, help
>
> Bernard
>
> Thanks,  I have been taking the presuure readings per Probst and the meter
> instructions; the meter goes between the fuel dist and the warm up
regulator
> (aka control pressure reg).
>
> I reran the test again tonite, both pre and post a new fuel filter.  Same
> numbers, both ways.  There was a short (1-2sec) spike up to 70# but that
was it,
> then the numbers held at 40-50#.
>
> I had hoped to put the meter on the end of the fuel filter, to see if the
pump
> alone was capable of reaching higher pressures, but unfortunately the
meter kit
> I got (J C Whitney special) does not have that fitting.  I am going to try
and
> find or fabricate this fitting.  I think it could be the decisive test as
to
> whether or not the pump can cut it, or whether as Ben Swann suggested in
another
> post (and you mention), the problem lies in the pressure reg.  It seem
that the
> problem is most likely one of these two...
>
> AFWIW, when i drained the gas out of the old filter, it was mstly clean,
but
> towards the end a cloud of fine black "stuff" came out of the dirty side.
> Possibly that fuel tank liner thing clogging the pump intake.
>
> Did not get to do the flow test, as it was getting dark, will hopefully
get
> there tomorrow.
>
> Agreed on the plugs, obviously a short term thing, probably as I was
limping
> home before if finally died.  Not a biggie as under the thin layer of
soot, the
> plugs looked fine.  But as I read Probst (and I've been doing that alot
lately
> ;-) lower fuel pressure does enrich the mixture, odd as it seems.
>
> Several have said that the additional pressure on the air plate is normal,
so I
> guess I got excited over nothing on this.
>
> Hopefully another day of testing will turn up the smoking gun; if not,
pretty
> soon I'll have to cry uncle and call in the experts.
>
>
> Steve
>
>
>
> Bernard Littau wrote:
>
> > Hi Steve,
> >
> > I'm no expert, but I have read the Probst book on the Bosch CIS.  I have
> > also had to deal with a low fuel pressure problem on my car -- with
major
> > help from local listers, including the loan of the Probst book :-)
> >
> > Fuel pressure should be much higher than 40 or 50 pounds; closer to 90.
> > Where are you measuring the pressure?
> >
> > This is correct behavior.  The fuel pressure pushes on the plunger,
making
> > it harder to raise.  They could have used a spring, but using fuel
pressure
> > instead of a spring helps to compensate for minor fuel pressure
differences,
> > and saves needing another calibrated spring.
> >
> > Plugs take some time to acquire a rich or lean condition.  It's likely
you
> > were running rich before your no-start situation.  A few cranks of the
car
> > won't change the plug's look.
> >
> > As above, the pressure on the plate is normal.
> >
> > I think you need to not link the fuel pressure to the plug condition.
The
> > fuel pressure is now, the plug condition is historical.
> >
> > Low fuel pressure is not going to make the car run rich, in fact, it
will
> > tend to make the car run lean.  This lean tendency can be compensated
for by
> > the ECU using the O2 sensor, so a car will typically run correctly even
with
> > somewhat low fuel pressure under moderate throttle conditions.  At high
> > throttle the car will stumble.
> >
> > Rich looking plugs are most likely to suggest a leak in the air intake
> > system -- the typical Michelin Man Hose leak is an example.  It seems to
me
> > that it would be difficult to check for small leaks in the vacuum or
intake
> > system with the car not running :-)  You may want to address this again
> > after the car is running.
> >