cdrmuetzel makes a good point about 'poisoning' the O2 sensor. This is also a concern for the automotive racing community, since they tend to use leaded fuels for high octane applications (like drag racing). Here is a quote from one of those forums "I use the innovate LM-1 with the Bosch sensor and we raced with it for 5 years, on VP C14 fuel (114 octane, leaded) , never had it alter its AFR reading. Engine is tuned well with tan on plugs and it runs at 12.8. Always powered it up, and I replaced it after 5 years for something to do, not because it was necessary, and the new sensor just read the same AFR as the old one, so the old one went into the box as a spare. So it is possible to obtain the time I said. And what I said about the 50 the 100 hours is what Bosch specify." So maybe the Buick sensor was more susceptable to contamination, or the engine was running too rich for that sensor. Definitely something to be addressed in such an application.

In response to steveinindy's comments - Q1- O2 sensors generate a voltage that is used by the EFI controller to regulate the A/F mixture. This voltage can be adjusted to provide control over the actual ratio (essentially tricking the EFI controller into giving the operator the ratio desired). Q2- The concept, whether using EFI or a carburetor, would be to provide mixture control to the pilot to get the desired engine conditions, just like mixture control and EGT are used today. Q3 - I think a lot of folks on this thread are over-thinking the question - O2 sensing can be used with a mixture control system of any kind to more accurately set the A/F ratio than using EGT. No fancy EFI or FADEC is required. This is just another sensor to help with engine management, and the original question was whether or not anyone had tried it. It sounds like a few have , with varied results. The biggest issue having been the leaded fuel potentially altering the readings.

Thank you everyone for your inputs, I think I have a grasp of the potential issues to be addressed. Finally, I have to admit that I'm truly amazed that, on a forum like this, there would be comments saying things like 'don't try something new, because others might try also it and screw things up'. To me, trying something new is what the spirit of the EAA is all about. Otherwise, this would just be the Cessna maintenance forum. Granted, you need to do your homework, and do your the best to mitigate risks. Can you imagine what life would be like if the Wright brothers heeded such advice?