I've heard that certain fuel additives or even exhaust flange sealants will
screw up your Ox Sensor.  I did run some Marvel Mystery Oil through my fuel
tank just for kicks once, and I used some kind of hardening sealant on my
joints when I installed my SS header kit.  Performance is not up to par, and
I'm wondering about that sensor.  Also, read on list about checking sensor
with volt meter.  Exactly which wires does one check on the 3 wire system?

Thanks
Brian Doss
'88 Weekender, Queequeg