CIS Diagnostic, help

[Steve Sherman]

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.
>