Wow!  What should a
"parts-replace-not-yet-promoted-to-backyard-mechanic"
do to learn the basics of the digifant system?  I have
a Bentley, but its the early model (copyright 84 or
85) that has precious little coverage of the
wasserboxer.

Thanks,
Ray

--- Coby Smolens <cobys@WELL.COM> wrote:
>
>     -----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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