So you o2 sensor is new. You didn't use any antisieze compounds on the
threads when you turned it in? You didn't get dirt on it or anything?
Good. So that green wire is co-axial. The outer wire is to isolate it from
any electrical noise (like the plug wire!) and the inner wire is the
important one. It is not uncommon for the outer wire to groun to the inner
wire. You may want to cut the wires back a ways, solder on a new inner
wire (forget the outer wire) and then connect it back to a good o2 sensor.

There is a way to check the continuity of the wire- Bentley spells it out-
which lead to check, etc. Also, see see if the center wire is common to
ground (not good! could be a bad wire then!)

With the o2 sensor disconnected i get about 18 mpg but am a tad weak in
power- with the o2 sensor connected i get 45% better (about 20-23mpg).

Good luck
matthew

Matthew Pollard          "Racing with the wind and flirting with death
Dept. Of Chemistry        So have a cup of coffee and catch your breath"
University of Idaho
www.uidaho.edu/~poll7356