RE: Snorkel boy (stirring the pot)

["Brian Honnold" <bhonnold@pac-cap.com>]

BBBBZZZZTtttttttttttt

We aren't talking about the function of the fuel distributor and I just read
the section you refer to which clearly covers only the function of the idle
mixture screw adjustment as it relates to adjusting the C0 content of the
exhaust at idle.

This discussion originated talking about Shannon's 16v and how he found a
"dramatic" increase throughout the rpm range after adjusting the IDLE
MIXTURE SCREW.....I believe with you and a test harness close at hand.

So that would mean that the discussion should focus on CIS-E cars where
99.9% of the mixture is controlled by the Differential pressure regulator
and the Oxygen Sensor circuit whenever the system is "off idle"

As I do happen to be sitting here with my early cis bentley on hand and my
Haynes (ack) covering all the fuel systems I feel I must speak first about
the early cis system

It is quite clear from the diagram in the Bentley that turning the IDLE
mixture screw changes the position of the control plunger, allowing more or
less fuel to enter the system at idle.  Reason states that if this plunger
moves, there should be a change throughout the rpm range dependent on the
position of the airflow plate.  However, and you should all be digging out
yer Bentleys by now because this is the most on topic thread on this list in
6 months, you can clearly see that there is a large "notch" in the plunger
that allows fuel to flow to the injectors when the metering plate is lifted.
Therefore, the miniscule amount that the idle mixture screw adjust the
plunger at idle will be negated by the massive changes in position as the
metering plate rises.

Now, the basic function of the system is the same for CIS-E equipt cars.
However, because this system incorporates the idle switch on the throttle
body which lets the computer and then the DPR know when the system is at
idle and the fact that the DPR operation off idle (and not at WOT) is
controlled by the 02 circuit and the temp circuit, any changes to the system
are automatically adjusted for when the system is off idle.  It would stand
to reason that the idle mixture setting would have little to no effect on
anything but idle.

I'm not doubting that the changes the Shannon made to his system greatly
improved drivability.  He stuffed in the 2.0 with a PP head and then went
about adjusting the system.  Any number of things from a sticking idle
switch on the TB to bad contacts on his temp circuit or fuel
module......could have been shaken loose and began working at the same time
he cranked the shit outta that adjustment screw.

It's all in fun guys, but if we are going to poke fun at each other and make
blanket statements, lets back them up with facts.

Brian Honnold
78 2.0 16v Turbo (third engine swap and 4th fuel system going in)
99 Passat GLX






> -----Original Message-----
> From: owner-scirocco-l@scirocco.org
> [mailto:owner-scirocco-l@scirocco.org]On Behalf Of Chris DeLong
> Sent: Friday, September 22, 2000 8:05 PM
> To: bhonnold@pac-cap.com; scirocco-l@scirocco.org
> Subject: RE: Snorkel boy (stirring the pot)
>
>
>
>
> Ok dude I will tell you how I "KNOW".
>
> Although I do not have the Bentley in front of me that covers
> MKII Scirocco
> I do know that the structure and function of the fuel
> distributor/air flow
> plate assy does not change with CIS cars.
>
> In the Bentley manual that covers '80-'84 Rabbit/Jetta/Scirocco
> on page 44
> of the Fuel and exhaust systems there is a perfect explanation
> and picture
> of the geometry and function of the fuel distributor.
>
> Feast on that. :-P


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