CIS Diagnostic, help

[Richard J. Andrews]

if i were you i'd get in the tank and seen what's floating around.
removing the screen will probably cure this problem. i had a 5k that did
the same thing

-rich
'86 4kq

At 09:40 PM 5/6/02, you wrote:
>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.
> >