Originally Posted by
mcaff
Posted by Gunter, one of the guys behind ECMSpy, in another forum:
QUOTE
From the Screamin Eagle manual "Closed Loop Bias adjusts the AFR control point from nominal. Note: Lower values (O2 voltage bias) will cause a leaner AFR. Higher values will cause a richer AFR."
QUOTE
That's pretty much plain bull****. Because it's impossible.
NB-O2 sensors are not made to and do not - I repeat: DO NOT - signal a specific mixture except lean (= O2 partial pressure higher than stoich) or rich (= O2 partial pressure lower than stoich). They won't as they can't. Especially not if it comes to a rich mixture. A NB-O2 sensor will also never ever signal constantly 0.50 volts or some other midpoint voltage , unless it's broken. Period, over and out. We have thousands of miles of wideband logging showing clearly, that there's no relation between NB-O2 voltage and mixture except the qualitative determination of being above or below stoich. Run away from people telling you something else, as they prove only having no clue of what they are talking about.
NB-O2 signal varies with O2 sensor temperature and O2 sensor age. A lean voltage of 0.12 volts (typ.) increases to about 0.20 volts, a rich voltage of 0.75 volts (typ.) drops to 0.65 volt. So it seems only reasonable to use an algorithm which is capable to cope with this situation. Every ECU I know of, evaluates only the voltage jump to trigger a EGO correction: if voltage is above rich threshold (~ 0.58 volts) fuel will be reduced, if voltage is below lean threshold (~ 0.42 volts), fuel will be increased. If voltage is between the rich and lean threshold, the signal will be evaluated as erraneous and be ignored. The impact of moving the "error range" on mixture is neglectable, because
a) NB-O2 sensors do not signal a voltage near the thresholds (unless defective) and
b) the integral factor of the PID regulator is chosen that way, that a voltage jump/mixture change is triggered much earlier.
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