Stiff Plunger in Fuel Distributor

[Jesse A Clendenning]

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[ Picked text/plain from multipart/alternative ]
 Rob, I agree with everything you've said. The only difference being that I=
 do not have a DPR either as my car is a turbo. We've both spoke of Control=
 Pressure as being the resistance to upward movement on the plunger. The re=
ference that Tom Chudzinski (thanks, excellent read) gave me, and the Bosch=
 fuel injection manuals that I own, part of the Fuel distributor is subject=
ed to System Pressure (supplied by fuel pump). This is where I was speculat=
ing that a failing fuel pump pushing much less pressure then normal could c=
ause a stiff plunger in the fuel distributor. The Warm up Regulator would s=
ection off the amount of pressure that it was set for ~3.5 bar. What was le=
ft would be in the other portion of the fuel distributor leaving a very unb=
alanced Air Flow Meter.  Let me know what you think.      I think I underst=
and what you are saying, but I don't think systempressure comes into it *di=
rectly* .  Its probably best to regard theresistance to upwards movement as=
 being related to control pressure. Lowercontrol pressure =3D less resistan=
ce to upwards movement =3D higher airplateposistion for given airflow =3D h=
igher plunger in dist =3D more fuel =3D richermixture.    Now as far as I k=
now control pressure is controlled by warm up reg andDPR only and remember =
that control pressure is derived by a calibratedorifice from system pressur=
e=2E There is thus a fixed supply of fuel andpressure to the control system=
. This is how the warm up reg works - whencold it bleeds off fuel in the co=
ntrol pressure system at a higher rate,leading to lower control pressure. H=
aving never had a car with a DPR (UKdweller) I can;t vouch for it but I gue=
ss the DPR does a similar thing toinfluence control pressure and hence mixt=
ure.    Now concerning the downward movement of the air plate, I think ther=
eshould not be any significant amount. If released the plate should movesma=
rtly back to rest with no hesitation, regardless of system or controlpressu=
re.    HTHrob> Message: 6> To: quattro at audifans.com> Subject: Stif=
f Plunger in Fuel Distributor> Reply-To: awdaudi at excite.com> From: "J=
esse A Clendenning" <awdaudi at excite.com>> Cc:> Date: Tue, 26 No=
v 2002 17:58:27 -0500 (EST)>>>> --> [ Picked text/plain from=
 multipart/alternative ]>> As I am still at work and do not have this=
 problem - as of yet, I wasthink=3D> ing... I've read a couple of posts =
about stiff control plungers in thefuel=3D>  distributor and have experi=
enced it once myself on an old 5000s. Mostpeop=3D> le assume that it is =
a result of the fuel pump running in an"overpressuriz=3D> ation mode." A=
fter thinking about this I believe that maybe this could bej=3D> ust the=
 opposite. The difference between the pressure on top of thedistrib=3D> =
utor and on the bottom of the distributor are what causes the pressure ont=
=3D> he plunger, correct? If there was excessive pressure on the bottom =
of thef=3D> uel distributor, wouldn't the plunger be easier to lift? Now=
 if thepressur=3D> e were low from a failing fuel pump - then pressure w=
ould be as high aspos=3D> sible on the top side of the fuel distributor,=
 and greatly reduced onbotto=3D> m side - making a stiff plunger.  In th=
e Bentley it describes cold control=3D> pressure (on top of fuel distrib=
utor) as being less than warm, making thep=3D> lunger move easier.  Does=
 this seem to coincide with your theories? or amI=3D>  flawed in my view=
s? I want to understand this better. Thanks, JesseClende=3D> nning>&g=
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