I built my own airfuel gauge using the schematic on that one site and it always showed rich, I used the potentiometer to change the scaling and it only came down from all the way rich when decelerating while in gear, then it never changed. I have a b16 so it has 2 o2 sensors so I tried running the ecu and the gauge off of the same one and now none of the lights are on (I know it works because right when I turn the key to on all the lights flash) and I get a code 1 from the ecu (o2 sensor). I used a test light I have and found that the o2 sensor going to the gauge and the ecu is grounded and the other one isn't (the light broke before I could check to see if the other one was positive). So today I switch the o2 sensors and I have the same problem. could my a/f gauge be killing my o2 sensors? is the o2 sensor supposed to be grounded?

 

I think o2 sensors are internally grouned which means they just get the ground from being in the metal of the exhaust.