Is the system at all similar to '80s watercooled vw's? (which use a single wire 02 sensor). I had 'brains' go bad in 2 early '80s vw's and the car would have no power and run very rough, the best solution seemed to be to unplug the o2 sensor. The cars ran great for several hundred thousand miles, power and mileage were as good as ever. It was a bit hard but not impossible to pass emissions. It seems to me to only go rich at idle (where the emissions problems were) and the exhaust would softly 'pop' when decellerating in gear. -it probably was a bit hard on the cat.

 

Should you ever read a negative voltage ?

I have mine wired into the cabin for an A/F and when I back off, it reads -0.13

Is this a sign of an iffy ground, or do they really go negative when super lean (fuel cut-off) ?