I would use a multimeter on the harness and test the output of the sensor while it is on the car. Then at least you might be able to track it down a little more.
I had a very similar issue once when tuning a car. Guy had just swapped over to 60# injectors, we go out for a drive after I change the tables, and there is no LTFT or O2 reading. Cant figure out what was wrong. Long story short it was a vacuum leak due to one of the injectors not being seated all the way in. Not saying that is for sure your issue. Just something you can check.
