From: "Jere & Beth Hawn" <jbrschawn@EARTHLINK.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, February 16, 2001 5:37 PM
Subject: FW: Inexpensive O2 Sensors - A Suggestion

> 2)      The way I understand this whole O2 thing is that it is a
binary value.
> Why not remove it from the exhaust, plug it, and simply put a switch
on the
> dash to flip when it starts running rough or when it is cold? (kind
of like
> an old fashion choke)

The O2 sensor functions to keep your fuel/air mixture *correct*
through a variety of operating conditions.

If you look at a graph of O2 sensor output compared to the fuel/air
mixture it looks like an "S" with a *very steep* (almost vertical)
middle section.  When the mixture is lean it puts out low volts (say,
.1, .2 volts) and when the mixture is rich it puts out higher volts
(say, .9, 1.0 volts).  The "just right" mixture output is right around
.5 volts, and it's this part of the curve that's very steep.  So, in a
way, you can say the O2 sensor works as an "on/off" switch, jumping
back and forth across that steep middle section from "too lean" to
"too rich."  But it does this continuously, allowing the ECU to make
adjustments "on the fly" and keeping the mixture in that middle range.

There's no way you can do this with an "on/off" switch on the dash,
and besides, how would you know if it should be "on" or "off?"

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Tom Young                      tomyoung1@home.com
Lafayette, CA 94549        '81 Vanagon
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