RE: 86 digifant running rich

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:

when I measure the O2 sensor = voltage, does it have to be disconnected from its mating wire? =
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).
When adjusting the airflow = mixture screw, does CW increase RICH setting and CCW increase LEAN setting?
For a given voltage setting, = say 0.5V, what is the fluctuation (dance) - is it +/- 0.15V
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