Proper Mixture.

[Alexander M. Lichstein]

Everybody should keep in mind that the (so called) lambda sensor is not
measuring O2 or A/F at all.  What it is is a galvanic cell which (at
temperature) will generate a voltage from EACH and EVERY component of the
exhaust gases.  The voltage contribution of each of these is proportional to
their partial pressures, as well as some constants relating to their size
(permittivity of the sensor), and their electronegative potential.  It so
happens that during normal combustion, the combined EMF's of exhaust gases
corresponding to 0.45V is about the stoichiometric limit.  As you get richer
from there, the different HC's present as well as the added CO etc. will
contribute unpredictably (at this point) to the voltage produced by the cell. 
This includes the different fuel components (aromatics, ene's, yne's, anes...)
which may be present, as well as the rate of drop-off of NOx production et. al.  
		If we could predict, at every temperature and operating
condition of THAT engine what these particular contributions would be, then we
could use these voltages in the rich (closer to 1V).  At this point in our
understanding of combustion, we are unable to predict these complex dynamics in
a general sense.  
		It may be that some of you have found that you can repeat
values which MAY correspond to exhaust compositions which correspond to
desirable A/F ratios under AVERAGE conditions, but these should not be
considered "REAL". 

		There is a really dense SAE paper about this topic which is a
good read.... number to follow.

		Don't lose heart though... some of these averaging and
"slurring" routines and filters may give an indication and could be useful for
set-up as environmental conditions change.  Further the sensors are real good
at telling you to which extreme you are if things just aren't right.

- Zander

Feel free to shoot me down.  I need to know more for my project.