My question (finally) is:  what O2 sensor output range is considered =
normal with the ECU adjusting things?  I thought that the O2 sensor / =
ECU combination attempts to adjust for no excess oxygen or a 0.00 =
voltage

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0.450 volts is about 14:7 Air fuel ratio, or stoichiometric.  So you want to
see about 1/2 volt, not zero volts.  Someone will correct me if I'm wrong
about the exact numbers.

I too have spent many months monitoring the O2 sensor.  In my case it is to
adjust the propane fuel system on my van.
Anyways, on gasoline I find that it moves between 0.500 - 0.800 volts in
closed loop.  I have wondered if it is on the rich side.
 The digifant seems to fluctuate in a very wide band, and be very erratic
compared to other vehicles I have monitored.
My 1986 Jetta CIS-E moves between 0.400 - 0.600 volts.
OBD II Japanese cars are tighter.

I find that I can lean the propane system right down to 0.050 volts (almost
16:1) at highway speeds with only a small reduction in power.  Fuel
consumption does not seem any better so theres no point. Some emissions may
be off the chart at that ratio though.  EGT is the same or slightly cooler
by about 100 degrees F on propane  So going very lean on propane does not
seem to affect cylinder head temp/EGT.

Another observation, O2 sensor output voltage on propane without feedback is
very stable, moves very slowly compared to gasoline.

I can't wait till there is a better (cheap for DIY) way to measure Air Fuel
ratio. I don't find that the oxygen sensor - voltmeter way is telling me all
that I want to know.
The UEGO sensors and infrared meters are too expensive as far as I know.
With tighter emissions requirments every few years, I'm sure something will
trickle down.

Also, I have

Gary Lee
Calgary