I installed a nifty air/fuel ratio meter on my 92 Volvo 740. Before
it goes colsed loop, it read 17.0 and pretty stable. It is obvious
when the car goes closed loop, as it then varies a lot. It takes a
measurement of the O2 sensor about once a second. I noted, at idle,
that the high is 19.5 and the low is 14.3. But it might be a false
assumption to take the median value as the average mixture reading...I
don't know. I see that Chevron says that stoiciometric for regular
unleaded gas is 14.7...at least for their brand. But I would think
that all gas would be somewhere close to this. SInce the low reading
is so close to 14.7, and the high is so much higher, I am thinking
that it is showing a lean condition. THe instructions that came with
the gauge don't tell you how to interpret the readings! But the gauge
is clearly marked AIR/FUEL. So I think it is saying the air/fuel
ratio is X parts AIR relative to 1 part fuel. But the way my Volvo
wagon eats gas, I SERIOUSLY doubt it is actually running lean!