Date:         Sat, 3 Feb 2001 19:01:14 -0800
Reply-To:     Tom Young <tomyoung1@HOME.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tom Young <tomyoung1@HOME.COM>
Subject:      Re: O2 Sensor Voltage
Comments: To: Mark Keller <tyler@ISLANDNET.COM>
Content-Type: text/plain; charset="iso-8859-1"

From: "Mark Keller" <tyler@ISLANDNET.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, February 03, 2001 3:44 PM
Subject: Re: O2 Sensor Voltage


> In other words if the fuel injection system is in proper
> adjustment, you should be able to disconnect the O2 sensor, and read
the
> voltage from the O2 sensor black wire.  Open loop voltage is very
stable
> and should be in the .5 volt range.

I'm not sure this is correct.  Doesn't "open loop" mean the ECU isn't
receiving a signal from the O2 sensor, and operating in its "default"
mode?  Once the O2 sensor is sending a signal, the ECU goes into
"closed loop" mode, meaning it's using the voltage generated by the
sensor, which is in turn affecting the sensor's voltage.

If you look at a graph of O2 voltage output vs. air/fuel ratio you see
a reversed "S"-shape  which is *very* steep right around the "correct"
output.  In other words, very *unstable.*

What you may be thinking of here is that in a correctly adjusted
system CO output (as measured by a gas analyzer) will be just about
the same with the O2 sensor connected as with it disconnected, thereby
giving the maximum range of adjustment.
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Tom Young                      tomyoung1@home.com
Lafayette, CA 94549        '81 Vanagon
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