I have an EB 6 cyl I have recently picked up for my wife and ther previous owner put in extractors and ended up getting an O2 sensor from the wreckers for it.

The car seemed to be going through a great deal of fuel. There was a strong fuel smell in the exhaust and the pipe was dark sooty.

My sensor has three wires - a black and two white.

I stuck a pin in each of them and measured the voltage with a hot engine.
One White is 14.49v
Black is .65v (this started at .4v and slowly went up
The other White is a constant .04v

Because there is a strong fuel smell in the exhaust I suspect that the sensor is working pumping out .65v

Can anyone please tell me where to go from here?

the white wire with 14v is ignition power the other white wire is an earth and the black wire is the signal wire to the ecu its voltage should be between 0.1V - 0.8V with Engine Running. so it sounds like its within its operating range.
otherwise have you looked at things like air filter? as a dirty or clogged air filter can also cause it to run rich.

whos to say the wreakers O2 wasnt f**k? why not buy a new one? what was wrong with the old one?

black is meant to be earth (i think. if its .4v-.65) that means the reading will be WAY out. i'd do it right and put a new sensor in for starters and maybe check the earthing.

the black wire at the o2 sensor is definatly signal to the ecu.
the other 2 white ones are power for the heated eliment and earth for the eliment..
although at the loom plug the wires change colour.
the black wire from 02 changes to blue/green at the plug..ecu signal
one white wire from o2 changes to grey/yellow at the plug.. + ignition
other white wire from o2 changes to black at the plug..- ground
i just wired in a ba 4 wire into my ed and that was how it was configured..

Thanks for the advice - I just removed the air filter and tested the black wire voltage - It maxed out at .63v
I put the air filter back and tested again - same voltage.

The previous owner of the car thought he was improving engine efficiency with putting on extractors. I noticed that each group of three cylinder outlets converge into a single pipe, then these two pipes converge into a single exhaust pipe. The O2 sensor is on only one of the two converging pipes so it will not be sensing the total O2 output. Would this have anything to do with the .63v reading? I thought best operating range was .35v to .4v

remember the ford falcon does run a little rich compared to other efi cars.
there are a few things that can contribute to the 02 readings.
you must understand that the 02 sensor will not respond straight away to removing the air filter.
the factory o2 is a (narrowband type) a rather primative device and will only give a rich or lean reading to the ecu. the .63 volt is on the rich side of the scale meening the o2 is reading a rich mixture, so its up to the ecu to adjust this mixture if the ecu connot adjust this mixture maybe look at a new air filter or new spark plugs.
the best thing to do is run a diagnostic on the ecu and see if you get any fault codes?
if you want to spend about $70 on a new 02 sensor and try it but it might not make much of a difference.
on another not if your engine temp is on the cold side the engine will run richer than usual.

also what condition is the engine in? if its starting to burn oil or getting low on compression it wont be able to run as efficient as it once did.

I believe the O2 sensor would not be affected by this. It doesn't need the total volume, just a smell...

An EB, or even EL for that matter o2 sensor is the best part of 10 years old,
It would be good practise to spend the $80 odd (or less) and replace it with a new one.

Other things to check, are coolant temp sensor, and map sensor or the hose.