Sensor voltage [mV] vs mixture (lambda)
Same thing, zoomed to best power area
These figures are exactly correct for one sensor type, with
a certain input resistance on the voltmeter, at one temperature etc etc etc.
My personal experience is that around 930-940mV is desirable, over 980mV
can cause misfiring at part load, and below 890mV increases the possibility
of knock. According to these graphs, these voltages correspond to
mixtures of .77-.78, .73, .85. I have a feeling that these are actually
leaner than that. My sensor is a Nippondenso one, single wire (not heated, that
is), about 30cm after turbo. Measured with a DVM, 1Mohm input resistance.