Date:         Sun, 4 Feb 2001 13:38:21 -0700
Reply-To:     Mark Keller <tyler@ISLANDNET.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Mark Keller <tyler@ISLANDNET.COM>
Subject:      O2 sensor clarications
Content-Type: text/plain; charset=us-ascii

I apologize that being on digest, I've taken a while to catch up on this
thread,.

The issue of O2 voltages is somewhat misleading and I'm trying to clear
up misconceptions about how the ECM actually functions when setting the
fuel pulse.  The ECM does not need the O2 sensor in order to set a fuel
mixture that is adequate.  The O2 sensor, in my opinion, is really a
safety valve for the catalytic converter.  One of the catalytic
convertors primary functions is to burn any remaining fuel or
Hydrocarbons, but too much unburned fuel will melt a catalytic
convertor.

The O2 sensor then limits the fuel mixture by giving the ECU a voltage
that in turn is used to ADJUST the basic fuel pulse.  If you have a car
with a convertor it's best to have a functioning O2 sensor.

The ability of the ECM to set mixture with: Temp II,  RPM, AFM and a
dependent fuel pressure value of 29- 36 Psi is very accurate.  When I
disconnect the O2 sensor and monitor it's voltage while driving at a
steady throttle setting  I observe a very steady reading on my digital
voltmeter. It changes to be sure, but the great majority of the time the
voltage is around .7 volts with the hundredths of a volt numbers varying
slowly. Changing the throttle setting will cause movement to a new
voltage but the same pattern of a steady reading occurs.

Sincerely,

Mark Keller
91 Carat