O2 sensor readings, DB

[RWestra@xxxxxxx]

Thanks guys for the very interesting insight into Oxygen sensors.
I have one additional question.  What prompts the computer to 
switch from open loop to closed loop?  Does it stay in open loop
until it receives signals from the O2 sensor or is it prompted by
some other input that the engine is warm enough to run in closed
loop operation?

The reason for asking is that my 81 "stalling during warm up" 
problem seems to occur at about the time I would expect the 
O2 sensor to begin to operate.  Obviously this is a guess but 
stalling seems to occur sometime between 5 and 15 minutes 
after starting cold.  It seems to vary depending upon engine load.
The heavier the load the earlier stalling begins.  I am about to
change the O2 sensor but I am not really convinced that is my 
problem.  

                                        Rolland Westra