RomRaider

I have a few of http://www.14point7.com/products/slc-oem these guys laying around from megasquirt builds, and got to wondering if its possible to improve the stock ecu's AFR resolution?

The SLC OEM has a linear output with the following reference points 0[v] @ 0.68 Lambda linear to 5[v] @ 1.36 Lambda.

our ecus use mA, not volts for determining front 02 AFR. 0ma = 1 lambda, unless the table is modified. otherwise, wideband controller input would have been used for full time closed loop by now.

32bit ECUs use a different sensor, and the values are smaller but the axis for the table is still in mA

I was thinking recently about placing WBO2 in place of stock. This is what i came to.

O2 sensor by itself does not generate electricity. It only changes resistance depending on the O2 concentration. ECU cannot measure resistance directly, so it uses a reference voltage and Ohm's law. I think that 0 mA in ECU's O2 calibration map means next: ECU submits a reference voltage (5V, if I'm not mistaken) with some known or, more likely calibrated amperage to O2 cuircuit. Then it measures amperage in a circuit. Of course, it drops by some value. This value is well known to manufacturer for every AFR because of standard stock O2 sensor. So, if circuit's current is X mA for AFR 14.7, then when current is Y mA, ECU simply subtracts X from Y and look up sensor scaling table. Say, Y-X=0.53 mA which corresponds 18.25 AFR.

So, I think it is possible to convert V calibration table to mA calibration table by measuring ECU reference current, measuring resistance of WBO2 sensor for different AFRs and doing simple calculations.

But actually you do not need a real wideband in place of stock. At 14.7 AFR stock O2 sensor is really good, maybe even better then most widebands. Moreover, in practice O2 sensor is used only when car is in closed loop to correct AFR deviations from 14.7 AFR. It is not used in open loop for correction - amount of fuel is calculated based on MAF sensor readings. So, you need WBO2 only for tuning/troubleshooting, not for everyday on-road use.

If you are using an Openport 2 cable you can connect the SLC VDC to pin 8 and use the standalone logging feature to read and convert to AFR.
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