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You'll have to excuse the attrocious grammer. Guess, I should have read over it before I posted. Anyways, I wanted to add something.
The LED guages trigger the next LED once the signal level hits the next higher or lower level. On a ten segment guage that is every .1V. On the Autometer that is every .05V. There is no indication in between. So, if the signal level is .89V than only the 8th LED will be lit and until the level tops .90V the 9th LED will not light. To be honest this is just find most of the time as the guage is bouncing around as long as the car is in closed loop control. When it becomes a bit more of a problem is at WOT. Is the car running at .80V or .89V? Even then anything over .8V is just fine and indicates a fairly rich condition but some small amount of power could be tuned into the car by reducing the ratio from .89 to .8V or more safety could be tuned in by increasing the ratio. Then back to my original point, the stock O2 sensor even when new is not exactly a precision device but rather a simple indicator switch telling the ECU if the car is rich or lean and not much more. In closed loop control like cruising on the freeway the guages will toggle rich/lean quite a bit. If the lean condition was as lean as some guages indicate it would be a serious problem. The other condition I have heard people complain about is near startup. Their car will indicate lean quite a bit as the O2 sensor is just not hot enough. The O2 sensors level varies quite a bit depending on temperature and becomes almost useless at less than 400F. Fortunately most sensors are heated as is my Saabs which takes some of the frustration out of the equation.
Well I've ranted plenty. There is gobs of info on O2 sensors and A/F ratio meters on the Web.
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