Date:         Wed, 13 May 1998 19:31:22 -0700
Reply-To:     David Bayer <bayer@SYBASE.COM>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         David Bayer <bayer@SYBASE.COM>
Subject:      Re: O2 sensor and CO adjustment
Comments: To: vanagon@vanagon.com

>| Should you set the CO (mixture) adjustment after installing a new O2 sensor?

        I think it depends on whether it had been adjusted as the old O2
sensor got replaced. This is just my own reasoning derived from the vanagon
Bentley, the Probst FI Bentley and my own dabbling with elecrtonics - I am
no expert on any of this so be forwarned, do your own logical checking, and
research.

        The fi system is based on electrical signals of parts that have
specified tolerances in their resistances. In a system with multiple parts
these variations add up, and there needs to a way to tune the system
to these differences as the system ages and parts are changed. Basicly I think
that screw is a small pot that I assume changes the resistance through the air
meter, air temp sender (I believe the digifant has one of these in the air
flow meter), or just through the 4th pin on the AFM connector (I can only think
of 3 pins being necessary for the afm and potentially an air temp sender).
This change in one of the signals changes the point in the mappings that the
ECU uses. It is used to adjust the baseline for the air fuel mixture around
which the O2 sensor will attempt to keep within limits as demands on the
engine change as specified by those mappings. One could check some of this
against the Bentley as I don't have it within 40 miles of where I am
correctly sitting ;)

        Now how does the O2 sensor then correct for large vaccuum leaks?
I don't know...

        Even if that isn't right - it's safest (but of course more expensive
to get the CO level adjusted).

dave