O2 Sensor Open/Close Loop

[kleenair at ix.netcom.com]

tom cloud wrote:
> 
>         [ snip ]
> 
> >  Now I was under the impression this was because of the O2 sensor
> >  temperature (and the temp effect on O2 sensor volts), not because of a
> >  different desired AFR.... The sensor is not very useful very far from
> >  stoich, so I don't think trying to stay in closed loop would buy you
> >  anything.
> 
>         [ snip s'more ]
> 
> I recently did some digging into O2 sensors, reading research and SAE
> papers.  From what I saw, O2 sensors, though very non-linear, are
> repeatable and do give meaningful results off stoich.  The argument
> was made on this group that exhaust byproducts other than O2, CO2,
> and H2O skewed the output making the reading off stoich meaningless.
> The stuff I read did not address this.  It did say that, off stoich,
> the temp of the sensor changed the reading (i.e. calibration), so
> it would not be accurate unless the temp of the sensor were factored
> into the measurement.  Now, Todd K. says that he regularly uses the
> EGO to help him tune his vehicles (that is what you said, isn't it,
> Todd?), and I faithfully watch the digital readout from mine when
> I tune my Bronco -- but I'm by no means an authority.  I just play,
> but it seems to me to give "useful" readings off stoich.  In other
> words, I feel that I can set my engine to give an EGO reading of
> about .8 volts or so for power and maybe .1 to .2 for economy.
> 
> Flame on.
> 
> Tom Cloud <cloud at peaches.ph.utexas.edu>

>From what I've read at various places, both Tom and Snip are correct, 
however, it is difficult to verify what the optimal voltage is on the 
engine without verifying it on a dyno.  Also all of this is assuming we 
have good fuel distribution from cylinder to cylinder, because the sensor 
measures an average of what is comming down the pipe.
Regarding the target voltage, I have generally found that once my target 
voltage is outside of the 0.3 to 0.7 volt window, my feedback loop 
becomes unstable.  By "unstable" I mean that swings in emissions output 
of the engine begin to widen.