I have a 95 geo metro. It has a 4 wire O2 sensor. My millage has not been what I think it should be so I hooked a multimeter and a air/fuel mixture gauge up. The voltage and gauge fluctuate wildly from most lean to most rich. I am sure it is not a loose connection. Does this mean the O2 sensor is bad?
Like SVOboy says, narrowbands fluctuate all over the place. On my Saturn, mine fluctuates up and down all the time, but it seems to cheat from 14.6 and up after the engine's all warmed up. When I am in steady-state cruising, the swing is much smaller, maybe 14.6 to 14.9 most of the time.
EDIT : Correction, the 14.6 to 14.9 is the digital/numeric display sample over a longer time period. So I still see the fluctuation. If I get a chance, I will make a youtube of it.
Thanks for the replies. I guess that little gauge is useless then so back it goes. I am only getting about 41 mpg out of this car and am stumped. I have changed the plugs, dist. cap, and wires. New filters and all to no avail. Any ideas?