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Originally Posted by Richard L
I am not sure if the design principle of WB is any different to the normal Lambda sensor. I believe they both detect excess oxygen and then calculate lambda value for displaying purposes.
So before going further, we need to establish the above before venturing further based on assiumption of WB actually detecting AFR and not excess oxygen.
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I believe that this is the case. I base that upon the design & documentation of both the Innovate LC-1 and the AEM UEGO.
In the configuration software for the LC-1, there is a screen where you tell the system what fuel you are using. A screenshot is attached:
Note that it says
"... to calculate AFR from Lambda", suggesting that the sensor itself responds to lambda.
In the documentation for that section, of the software, it states the following:
On this page you can see the software version of the LC-1 and you can change the multiplier to
calculate AFR from Lambda. A number of different multipliers are already pre-selectable but you
can change it to a custom one for the particular fuel you are using.
So from this, I infer that the LC-1's sensor element responds to lambda (which would be a constant for the stoichiometric ratio of any fuel) and then relies upon this setting to determine the correct multiplier it will use to convert that lambda value to an AFR value for display purposes.
The AEM gauge is much less configurable, and the documentation is not quite as clear. It does state that
"UEGO sensors use a ?current pump? to determine the actual oxygen concentration within the sensing element" and in the "specifications" section in the back, it indicates
"Measuring Range: 0.751 to 1.143 Lambda". Additionally, it notes that of the five switch-selectable calibrations, four are intended for use with gasoline, and implies that if an alternate fuel is used, the fifth calibration, lambda, should be selected. It then lists a table of the 1λ values for various fuels, along with a table showing what AFRs corresponds to the range of 0-5v output for all those fuels. In every case, the 1λ point for each fuel occurs at 2.35v, despite the fact that there is no user-selectable calibration for discriminating between, say, ethanol, methanol, propane or CNG. One is simply presumed to have selected the lambda display calibration for any non-gasoline fuel.
So I believe it to be a safe assumption that, like their nernst-cell cousins, wideband O2 systems natively respond to lambda. What I don't know is whether this validates my belief that, assuming an "ideal" (meaning best power) AFR is 12.5:1 for gasoline, and 5.5:1 for methanol (both equating to 0.85λ) does it follow that tuning for a displayed value of 12.5:1 on a sensor calibrated for gasoline, which we presume to indicate 0.85λ regardless of the specific fuel involved, is optimal for a blend of two fuels (gasoline and methanol) at a ratio that is not precisely known.