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Date:         Thu, 3 Jun 1999 06:32:31 -0700
Reply-To:     "M.R. Nimmo" <mrnimmo@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "M.R. Nimmo" <mrnimmo@YAHOO.COM>
Subject:      Re: 86 digifant running rich
Comments: To: vanagon@vanagon.com
Content-Type: text/plain; charset=us-ascii

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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