Date:         Thu, 3 Jun 1999 03:52:33 -0700
Reply-To:     Coby Smolens <cobys@WELL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Coby Smolens <cobys@WELL.COM>
Subject:      Re: 86 digifant running rich
Content-Type: multipart/alternative;


    -----Original Message-----
    From: Coby Smolens [mailto:cobys@well.com]
    Sent: Thursday, June 03, 1999 1:40 AM
    To: PhamA
    Subject: RE: 86 digifant running rich


    Glad if I can provide anything of use --

    You wrote:
    "I always would like to know how to check and set my CO without having
the $20K instrument."

    In fact I'm not sure you can, exactly. With the O2 sensor plugged in
your going to get this wild swinging reading from .2-.8V, which is not going
to allow you to accurately set the initial mixture. The prescibed method
calls for unplugging the sensor and setting the CO to .7% +/- .4%. I suppose
one could measure the precise voltage output of a new O2 sensor in a known
clean/smooth running van and adjust the mixture on another van to obtain the
same voltage, but I never had to do it that way, so I have no data to
support such a hypothesis. I may try it sometime, just out of curiosity. It
would be handy to be able to do this adjustment in the absense of a pricy
machine. After all, when the O2 sensor is in closed loop operation (plugged
in), the ECU takes over and makes all corrections, provided the initial
setting is in the ball park. The first couple times I worked on the 'Fant I
watched the system correct the mixture to perfectly clean running while I
purposely tampered with the mixture adjustment in a vain attempt to richen
an apparently too-lean running condition...

     You wrote:
     "When I measure the O2 sensor voltage, does it have to be disconnected
from its mating wire?"

    No. If it's disconnected, you get only the raw output from the sensor,
not the "crosscounts" that indicate the ECU is enriching and leaning the
fuel mixture.

    You wrote:
     "What is the nominal setting for an '84 1.9L , 0.2v or 0.8v? Does LEAN
setting mean closer to 0.2V (for airplane, they measure the temperature of
the exhaust.  If all O2 is burned completely, the engine runs hotter and so
on)."

    The nominal response from the O2 sensor to the fluctuations in fuel
mixture generated by the ECU is to send  higher voltage signal as the
mixture goes rich and a lower one as the mixture goes lean. As the ECU gets
the higher voltage signal it trims the mixture, until the sensor responds to
the lack of O2 and the voltage drops to the low side (voltage is generated
by an electro-chemical reaction which occurs in the presence of oxygen). The
ECU picks up the change and richens the mixture until it receives the high V
again, etc., etc., etc. The nominal _range_ of this fluctuation cycle from
high to low and back and is from near zero to near 1V, at a frequency of
one-two times/second. This is how the computer attempts to achieve the
mythical "lambda" state, or an air/fuel ratio of 13.7:1 (I'm not sure if I'm
correct as to the exact number, but it's in that vicinity.) Lambda is to an
ECU what pi is to a theoretical mathematician - an unreachable number, but
that doesn't stop 'em from trying!

    You wrote:
    "When adjusting the airflow mixture screw, does CW increase RICH setting
and CCW increase LEAN setting?"

    CW (tight) is rich, CCW (loose), lean.

    You wrote:
    "For a given voltage setting, say 0.5V, what is the fluctuation
(dance) - is it +/- 0.15V"

    Again - there is no specific voltage "setting". The voltage is going to
fluctuate constantly between .2V(+/-.15V) and .8V(+/-.15) in a healthy
system at full op. temp. running at 2000rpm, and it is going to do this one
to two times per second.

    You wrote:
    "Can you advise the timing setting?"

    Setting the timing on a 'Fant is an arcane procedure. I recommend
getting the Bentley book and using it as a reference. But basically: Warm
engine to norm.op.temp., disconnect temp sensor #2 (at the thermostat
housing, blue plug), run engine at 2000rpm and measure advance using a
digital advance type timing light. Reconnect T2 sensor, run engine to 3000,
measure timing. I have to check the book every time I do this, but I believe
the numbers are

    Coby Smolens, Owner
    Valley Wagonworks
    VW Bus and Vanagon Repair
    1535 Sir Francis Drake Blvd.
    San Anselmo, CA 94960
    415 457-5628
    http://wagonworks.com


        -----Original Message-----
        From: PhamA [mailto:PhamA@aurorabio.com]
        Sent: Wednesday, June 02, 1999 11:47 AM
        To: 'Coby Smolens'
        Subject: RE: 86 digifant running rich


        Coby,
        Thanks for posting this CO checking procedure.  I always would like
to know how to check and set my CO without having the $20K instrument.  This
is definitely excellent information and method.

        For clarification:

            1.. when I measure the O2 sensor voltage, does it have to be
disconnected from its mating wire?
            2.. What is the nominal setting for an '84 1.9L , 0.2v or 0.8v?
Does LEAN setting mean closer to 0.2V (for airplane, they measure the
temperature of the exhaust.  If all O2 is burned completely, the engine runs
hotter and so on).
            3.. When adjusting the airflow mixture screw, does CW increase
RICH setting and CCW increase LEAN setting?
            4.. For a given voltage setting, say 0.5V, what is the
fluctuation (dance) - is it +/- 0.15V
            5.. Can you advise the timing setting?

        Many thanks in advance.
        Cheers,



        Andrew Pham
        Aurora Biosciences Corp.
        11010 Torreyana Rd
        San Diego, CA 92121
        619-404-6614
        619-404-6726 fax
        phama@aurorabio.com


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