At 09:04 AM 1/24/2002 -0800, you wrote:
>You rang??
>
>Responding to D-square's inquiry:
Thanks Dick
>The O2 sensor will put out 0.45 volts at stociometric optimum air/fuel
>ratio. Lower voltage means leaner mixtures, and higher voltage means richer
>mixtures. You must use a very high impedance measuring device to read this
>voltage, I prefer to use an oscilloscope, but an electronic voltmeter with a
>probe impedance of 1 megohm/volt or better will give a fairly accurate
>reading.
Also, my understanding is that the standard O2 sensor has very rapid
voltage response with A/F. In other words, the output changes very rapidly
once you deviate some for the stoichiometric 14.7 and then stays more or
less constant at the high or low value regardless how lean or rich
respectively (I hope I didn't get it backwards) the mixture gets. That's
why for example modern cars run open loop at WOT, because the mixture is
rich enough to be beyond the sensitivity range of the O2 sensor, so the O2
sensor info is useless to the computer, and the injection pulse width is
based on the pre-programmed values only. The wide range sensor (far more
expensive) has a wider sensitivity range, but its used only in labs.
In this case, the sensor
>voltage goes lower than 0.45 volts. Usually the output range seen is 0.2 to
>0.7 volts.
Do you actually mean 0.07? 0.7>0.45! And yes, the sensor needs to be hot
before it can provide useful readings. That's why they install it as close
to the manifold as possible. The faster it will warm up, the faster the
engine can operate in closed loop. Sometimes the ECM runs the engine
retarded when cold started to increase exhaust temperature and accelerate
the sensor warm up.
D^2
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