ScanGauge O2 sensor values
 

When using an O2 sensor XGauge (from the XGauge examples PDF), the range is 0-99. How does one interpret the reading? What number would be stoich, which direction is lean/rich, and how far does it have to go before it's abnormally rich/lean?

I think jay did a lot with this to detect DFCO on his vehicle.

he may be a good resource

If you want to display A/F ratio, it's worth investigating whether you can program an A/F xgauge. I was able to get one working on my CAN protocol Scion, but not with my (older)ISO protocol Nissan.

Unfortunately, the A/F display isn't very helpful. The leanest ratio I've seen so far in limited testing is 14.6:1. It goes to 18.9 with the engine off. I think I'll try this wideband oxygen sensor.

I know I had an A/F XGauge working correctly once before, but I tried one yesterday and it didn't work. I was able to observe O2 data and I'd like to know what I saw.

I've tried the a/f xgauge, after a day or two I got bored with it. The number doesn't change much on my vehicle, maybe by .1 every once in a while. The O2 sensor reading will be 0 in DFCO. In most driving it will be in the 50's-60's. The highest I ever recall the reading being is 80 or 81.

-Jay

So when it was 80 or 81, was it rich or lean?

THe higher the number, the richer the exhaust. For some reason the o2 reading spikes to 79 or 80 a fraction of a second before DFCO kicks in. I have no idea why though.