Stiff Plunger in Fuel Distributor

[Jesse A Clendenning]

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[ Picked text/plain from multipart/alternative ]
  Rob, It always helps to talk this stuff through. I see now and you are ab=
solutely correct. Thanks for helping me out. CIS is clearer to me by the da=
y=2E   Sincerely, Jesse Clendenning        Hi Jesse,    Well I think you're=
 well into the 1% of the global population whounderstand the basics of the =
K-jet fuel distributor. However please forgetabout system pressure as far a=
s resistance to the  movement of the air plateis concerned. You are correct=
 to say that system pressure is present in thefuel distributor. It is of co=
urse regulated by the (usually?) integralpressure regulator. It is the moti=
ve force for all movement of fuel to theinjectors and is present in full to=
 the chambers of the lower half of eachport (below the diaphragm ) and to t=
he CSV. Also central to the meteringsystem  are the pressure regulating val=
ves that ensure that the quantity ofmetered fuel supplied to the injectors =
is governed solely by the position ofthe plunger rather than any significan=
t pressure diferential between top andbottom chambers. So give or take a fe=
w psi system pressure is present rightthrough to the injectors. The crucial=
 point to note is that it is controlpressure only which is used to oppose t=
he upward movement of the plunger andhence air plate. When I say 'oppose th=
e upward movement' it may be easier tovisualize it as having a certain 'wei=
ght' depending on CP.    If this were not the case then the scenario you ar=
e thinking about wouldindeed be a problem. If the pressures on either side =
of the diapraghm weresignificantly different it would be easy to imagine a =
situation where itwould be difficult to stop the flow of fuel to the inject=
ors, - bit like thedifference between holding your finger in a hole in a da=
m, compared to thedifficulty in stopping the flow once you've taken it out!=
    From what Tigran was saying it sounds very much like his fule dist has =
aproblem, maybe related to the DPR. There should be no significant resistan=
ceto the downward movement of the air plate, and smooth steady resistance o=
nthe way up, the strength of which is related to the control pressure. Anyo=
newho wants to see it demonstrated can get a pressure gauge, plumb it into =
thefeed to the warm-up reg and jumper the FPR. Then with an electrical supp=
lyto the bi-metallic strip in the warm-up reg, play with the air plate andf=
eel it get harder to lift as the warm up reg gradually increases controlpre=
ssure.    Okay, hope this helps get you in the picture, if not let me know,=
 we'llget this straight in the end!rob----- Original Message ----- > Mes=
sage: 6> To: quattro at audifans.com> Subject: Re: Stiff Plunger in Fuel=
 Distributor> Reply-To: awdaudi at excite.com> From: "Jesse A Clendennin=
g" <awdaudi at excite.com>> Cc:> Date: Wed, 27 Nov 2002 10:46:29 -=
0500 (EST)>>>> --> [ Picked text/plain from multipart/altern=
ative ]>  Rob, I agree with everything you've said. The only difference =
being thatI=3D>  do not have a DPR either as my car is a turbo. We've bo=
th spoke ofControl=3D>  Pressure as being the resistance to upward movem=
ent on the plunger. There=3D> ference that Tom Chudzinski (thanks, excel=
lent read) gave me, and theBosch=3D>  fuel injection manuals that I own,=
 part of the Fuel distributor issubject=3D> ed to System Pressure (suppl=
ied by fuel pump). This is where I wasspeculat=3D> ing that a failing fu=
el pump pushing much less pressure then normal couldc=3D> ause a stiff p=
lunger in the fuel distributor. The Warm up Regulator woulds=3D> ection =
off the amount of pressure that it was set for ~3.5 bar. What wasle=3D> =
ft would be in the other portion of the fuel distributor leaving a veryunb=
=3D> alanced Air Flow Meter.  Let me know what you think.      I think I=
underst=3D> and what you are saying, but I don't think systempressure co=
mes into it*di=3D> rectly* .  Its probably best to regard theresistance =
to upwards movementas=3D>  being related to control pressure. Lowercontr=
ol pressure =3D3D lessresistan=3D> ce to upwards movement =3D3D higher a=
irplateposistion for given airflow =3D3Dh=3D> igher plunger in dist =3D3=
D more fuel =3D3D richermixture.    Now as far as Ik=3D> now control pre=
ssure is controlled by warm up reg andDPR only and remember=3D> that con=
trol pressure is derived by a calibratedorifice from systempressur=3D> e=
=3D2E There is thus a fixed supply of fuel andpressure to the controlsystem=
=3D> . This is how the warm up reg works - whencold it bleeds off fuel i=
n theco=3D> ntrol pressure system at a higher rate,leading to lower cont=
rol pressure.H=3D> aving never had a car with a DPR (UKdweller) I can;t =
vouch for it but Igue=3D> ss the DPR does a similar thing toinfluence co=
ntrol pressure and hencemixt=3D> ure.    Now concerning the downward mov=
ement of the air plate, I thinkther=3D> eshould not be any significant a=
mount. If released the plate shouldmovesma=3D> rtly back to rest with no=
 hesitation, regardless of system orcontrolpressu=3D> re.    HTHrob&=
gt; Message: 6> To: quattro at audifans.com> Subject:Stif=3D>=
 f Plunger in Fuel Distributor> Reply-To: awdaudi at excite.com>=
 From:"J=3D> esse A Clendenning" <awdaudi at excite.com>&=
gt; Cc:> Date: Tue, 26No=3D> v 2002 17:58:27 -0500 (EST)>&=
amp;gt;>> --> [ Picked text/plainfrom=3D>  multipar=
t/alternative ]>> As I am still at work and do not havethis=
=3D>  problem - as of yet, I wasthink=3D3D> ing... I've read a co=
uple of posts=3D> about stiff control plungers in thefuel=3D3D>  =
distributor and haveexperi=3D> enced it once myself on an old 5000s. Mos=
tpeop=3D3D> le assume that it is=3D> a result of the fuel pump ru=
nning in an"overpressuriz=3D3D> ation mode."A=3D> fter thinking a=
bout this I believe that maybe this could bej=3D3D> ustthe=3D>  o=
pposite. The difference between the pressure on top of thedistrib=3D3D&=
gt;=3D> utor and on the bottom of the distributor are what causes the pr=
essureont=3D> =3D3D> he plunger, correct? If there was excessive =
pressure on the bottom=3D> of thef=3D3D> uel distributor, wouldn'=
t the plunger be easier to lift?Now=3D>  if thepressur=3D3D> e we=
re low from a failing fuel pump - then pressurew=3D> ould be as high asp=
os=3D3D> sible on the top side of the fueldistributor,=3D>  and g=
reatly reduced onbotto=3D3D> m side - making a stiff plunger.  Inth=
=3D> e Bentley it describes cold control=3D3D> pressure (on top o=
f fueldistrib=3D> utor) as being less than warm, making thep=3D3D&gt=
; lunger move easier.Does=3D>  this seem to coincide with your theories?=
 or amI=3D3D>  flawed in myview=3D> s? I want to understand this =
better. Thanks, JesseClende=3D3D>nning>&g=3D> t; _____=
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