Sorry I can't provide the link but I'm working off the suggestion from an older thread in which a poster claimed the following:

"The high voltage means that all available oxygen is used in the exhaust gas, and therefore the dis-similar oxygen content from the exhaust side to the ambient air side generates the voltage - hence the engine is running rich. To test the O2 sensor, add air to the intake system, without causing a misfire. Remove the power brake hose and put your thumb over it. With the engine running, and while monitoring the O2, add a bit of air by lifting your thumb a small amount. If the sensor quickly shows a lower voltage, preferably below .200 volts, then it is probably OK, and you have confirmed that the fuel system is otherwise at fault. If the O2 won't respond, or get much below .300 volts, then it is faulty. It's a quick check, but it works. You may also find the engine smooths out."

That's an old thread and I don't wanna revive it, but I really gotta know just how this is done:
Is it the one at the front part of the brake booster that leads directly to the intake manifold?
Do I remove the hose before I start the car, or afterward?
Is there anything I have to do or worry about in removing the vacuum from my brake booster or is this really as easy as the poster suggested?


Only 14,000 more things to figure out from here. Thanks guys!!!

Where are you connecting the volt meter on the o2 sensor? at the plug connection?
Just asking as too on a 240 1991 would like to check with this method. Although my O2 is a three wire.
Thanks

Mine is also 3 wire, and it is thankfully right up in the exhaust manifold by the engine. I'm tapping it with an alligator clip to my multimeter and then grounding the other electrode of my meter on wherever I can reliably stick my needle without it falling out during the testing. some tests call for grounding the O2 sensor's black sender wire in order to check the ECU's response to its lack of communication.

Thanks for the details.
I'll be checking mine this weekend. Keep me posted on yors and maybe we can compare notes.
Thanks

Any additional air added past the AMM, will cause a leaner burn that will show up as a lowered voltage at the O2 sensor.

You could also pull the manifold hose to the passenger compartment that provides vacuum for the floor/windshield/recirculate air controls.

Done while engine running so you can observe changes.
--
1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

Where is that particular hose? Which side of the car does it pass through the firewall, passenger or driver?
thanks!

Look for a thin black tube that enters through the passenger side of the firewall. Follow it back to the intake manifold where it plugs into the larger plastic check valve and short hose on the manifold.
--
1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.