Some quick questions for yall. First I was wondering if anyone knew if the 2001 ford mustang 3.8l uses the downstream O2 sensors to determine air-fuel mix if the upstream ones are unplugged. Also for some reason, my mustang seems to run better when I unplug the upstream 02 sensor bank 1, but I have replaced this sensor twice now and it still seems to give me trouble. There is no sign of a vac leak and the head gaskets are new. Finally, after I cleared my car's computer I went on a test drive with only the bank 2 upstream o2 sensor plugged in and for some reason, the bank 1 o2 sensor spiked to -20% STFT for a minute, now the car didn't run rough or anything but it was concerning because I didn't have the bank 1 o2 sensor plugged in. Any help would be greatly appreciated! Thanks!!