Date:         Sun, 16 Jan 2000 08:39:57 -0500
Reply-To:     Lawrence Johnson <larry_avery.johnson@SYMPATICO.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Lawrence Johnson <larry_avery.johnson@SYMPATICO.CA>
Subject:      Re: Engine management (manual control of mixture)
Content-Type: text/plain; charset=us-ascii

David Marshall wrote:

> The O2 sensor is basically an exhaust temprature gauge.

The Oxygen Sensor senses oxygen, not temperature. It has to be hot itself
before it measures correctly but it does not measure temperature.

> Connecting a multimeter to your O2 sensor is a poor mans CO gauge.  You're
> right it is
> just a transistor with a user adjustable gain (loss) - a pretty simple
> device!

If you disconnect your OXS before starting the engine, the ECU resets to
default mode for air fuel mixture (equivalent to about .75 volts on the OXS)

If, however, you have the OXS connected when you start the engine and then
disconnect the OXS then the ECU still thinks that the OXS is there. If then
you ground the sensor wire to the chassis, then the ECU thinks that the fuel
mixture is too lean and will enrich it. With a voltmeter connected to the OXS,
you can read this rich state as a voltage near 1 volt. Alternatively, if you
connect the OXS to a 1 volt source (I used a rechargeable battery), then the
ECU thinks the mixture is too rich and the ECU will lean the mixture. With a
voltmeter connected to the OXS you will read a low voltage near 0 volts.

All of this, I have done with no ill effects (I have an MT cat).

I don't think that the air/fuel mixture set by the ECU based on the OXS
feedback (av. .5 v) is the optimal power setting. More than likely it is set
for minimum emissions. But I don't think that the default (.75 v) is the
optimal power setting either. I'd like to play around and find the sweet
point. My earlier suggestion of using a potentiometer and a 1 volt source to
fool the ECU was an attempt to force the ECU to use a setting which is richer
than with the OXS but leaner than the default. Hell, on the freeway you could
dial it to lean and in the mountains dial it to rich. You could attach the
voltmeter to you dash and watch the OXS just like I do with my Darrell-o-meter
connected to my Digifant ECU.

Its simple and cheap.
-Larry