Re: O2 Sensors

[RayVR4@aol.com]

The most inexpensive one I've seen is made by Cyberdyne (~$30) who also makes
a host of other digital gauges.  It comes with a 10 LED readout inside a 2
1/8" cup.  I know of at least one person who has dismantled it from the cup
and custom mounted the LED's into the instrument panel.  These gauges only
use a 12v wire, ground and sensor wire which taps into one of the ones on the
stock O2 sensor.  Cyberdyne gauges along with a wide variety of VDO and
Autometer gauges can be found at Summit Racing (216) 630-0200 or Jegs (800)
345-4545.

The O2 sensors on production cars are not very linear and are only sensitive
within a narrow range.  I'm not sure about the Audi, but because of this,
 most cars only use the O2 sensor for adjusting fuel for idle and part
throttle.  At WOT they then switch to a different fuel map based mostly on
the air mass sensor.  Stoich is right around .5-.6V    At WOT you'll want the
O2 to max out which will usually be between .85-.95V which corresponds to
13.1/1 or richer.  Under high boost conditions you'll probably want something
even richer but the O2 sensor won't give you that kind of accuracy.  If you
do find the voltage starting to drop at WOT it is, however, a warning that
you're leaning out.  In normal operation, the O2 sensor takes a minute or so
to warm up and start sending a signal after starting the car.  It will then
cycle between the current O2 voltage reading and 0V.  This cycling increases
in frequency with throttle and at WOT will stop cycling and stay at the O2
voltage reading.

To get more info you may consider getting an exhaust gas temp gauge which
will give you another indication of whether you're leaning out (~$150).

Ray