Introduction & O2 Sensor Questions

[James Boughton]

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Neil,
	As far as I can tell, the problem with using an oxygen sensor to do =
wide range fuel/air work is that they are not accurate in the rich =
region.  The cheapest system I am familiar with to do wide range =
measurement is $1000.00US.  The problem is that the partial pressure of =
oxygen in the exhaust is dependent on temperature on the rich side of =
stoichiometric.  For more information, consult John Heywood's book =
"Internal Combustion Engine Fundamentals", page 302, where you will also =
find a voltage output vs. lambda curve.
	Also, another error is introduced since the oxygen sensor functions =
according to the Nernst equation, which gives the voltage output of the =
oxygen sensor mainly as a function of partial pressure of oxygen in the =
exhaust and of temperature of the sensor.  Most oxygen sensors have no =
temperature compensation, which creates inaccuracies with typical =
production based oxygen sensor measurement systems.  Remember automotive =
manufacturers use this sensor mainly to determine where stoichiometric =
operation is.
	Let me know if this helps.  BTW, after calibrating engines with wide =
range sensors to get close, I have also used spark plug color to fine =
tune WOT operation on race days.  Make sure you consult a spark plug =
manufacturer rep. for their suggestions.  They can be quite helpful.

Jim Boughton
boughton at bignet.net

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From: 	Neil Poersch/MTSCom/MTS[SMTP:Neil_Poersch at mts.mb.ca]
Sent: 	Friday, July 04, 1997 4:58 AM
To: 	DIY_EFI
Subject: 	Introduction & O2 Sensor Questions

This of course meant that I had to revise all
the jetting in the carbs to accomodate the increased air flow.  I  did=20
this using the traditional method of observing spark plug color.  This
of course takes a lot of time so I thought  a better way might be to
monitor the output voltage of an oxygen sensor.  I am aware of the
unit which K&N sells but I thought it was very over-priced for what you
get.

I purchased a universal replacement O2 sensor (made by or at least=20
packaged and distributed by KEM Automotive Products), machined a=20
fitting and TIG welded it onto the crossover pipe on my exhaust.

I find that under normal running conditions I typically read about
0.9 to 1.0 volts from the sensor. From what I read about O2 sensors
this should indicate a very rich mixture however the engine seems to run
quite well and the plugs show a light tan colour.

I believe the sensor does respond to lean mixtures because when I
deliberately make the idle mixture overly lean I read 0.3 to 0.4 volts.
Also when I am running wide open throttle on the highway and snap the
throttle shut I momentarily read 0.1 to 0.2 volts until the carb =
responds to
the new conditions.

After all this rambling I guess my question is has anyone had any
experience in using an O2 sensor for monitoring fuel/air ratios?  Also
does anyone have any info on what the output voltage curve versus=20
fuel/air ratio should be?


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