i do know how it works. there's a 5v reference voltage from the ecu and a ground. the return signal is 4v or less, depending on elevation. the problem with the op is the ecu would have to be rechipped or something to get any NOTICEABLE change in mixture.

like ILUVMILS said, unplug it and see what change there is in running-none. at least here at sea level. found them unplugged many a time after someone installed an air filter in an e30 325. very easy to forget as once it's all together, the harness gets buried.

because it's free, that may the only motivation. this won't provide something for nothing. and so it goes, chuck.