CIS Diagnostic, help

[rob hod]

    Steve,

    Just reviewing three days worth of digest, I skimmend thru  your
previous post on this topic. In case you haven't had any help elsewhere let
me just explain that the movement of the air plate in the upwards direction
is opposed by the so called 'Control Pressure' in the the secondary circuit.
This is controlled in the main by the warm up regulator, and should vary
from around 1.5 bar on a cold engine up to maybe 4.5 on a warm engine (i'm
talking very generalized  figures). When you release the fuel system
pressure you also release the control cicuit pressure. In brief it's normal
for the air plate to move freely with no control pressure, and in a cold
engine , jumpered situation the plate should be more difficult to move
(upwards) than in a warm engine situation.

    Primary fuel pressure should be constant , where are you measuring it?

    in further experiments remember to check out the cold start circuit as a
possible cause of unintended richness!

    HTH

rob
----- Original Message ----- > Message: 7
> Date: Sun, 05 May 2002 19:00:38 -0600
> From: Steve Sherman <spsherm at attglobal.net>
> Reply-To: spsherm at attglobal.net
> To: quattro <quattro at audifans.com>
> Subject: CIS Diagnostic, help
>
> A bit more info on my 86 5KTQW that won't start (or stay running the few
> times it does catch)...
>
> Starts/runs if you feed it ether.  Checked for vacuum/hose leaks, but
> did not find any.  Spark plugs are sooty, from too much fuel not oil.
> Good compression, and crank, valves and dist are all in sync. Fuel pump
> works, but when I took a pressure reading, I got 40-50#'s; with quite
> alot of jumping around (that is it did not settle down at a steady
> pressure).  This is with the engine off and the fuel pump jumpered to
> run.  And FWIW, the air plate in the fuel distributor seems hard to move
> up, but comes down easily; up resistance goes away when fuel pressure is
> removed.
>
> I'm trying to add these all up to come up with a likely diagnosis, but
> seems like they are pointing in different directions...  The low/erratic
> fuel pressure would seem to say clogged fuel filter or bad pump.  But
> the sooty plugs and up pressure on the air plate seem to point to too
> high a fuel pressure.
>
> Anyone in list land an expert on the CIS system?  Could low or erratic
> fuel pressure cause rich running sometimes (sooty plugs) and no fuel
> situation others?  Other possibilities that fit these symptoms?
>
> TIA
>
> Steve
>
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