A/F/R gauge for tuning

92b said

I'm might not be thinking correctly but here is how I see it.
For this example there is no reversion. Air (oxygen) and fuel are drawn into the cylinder as a rich mixture. Enough to cause a misfire. During this cycle what would be left over is unburned fuel and oxygen. Of the two the o2 sensor only detects oxygen. Oxygen in a higher proportion than if normal combustion had occurred. I think the o2 sensor will read that as lean.
In order for reversion to cause the o2 sensor to read this as a rich mixture it would have to selectively reverse only the unburned fuel past the o2 sensor and none of the unburned oxygen. Diluting the left over oxygen to the point of reading rich.
Again I'm not saying this is right.

Click to expand...

Rich in, rich out. A missfire pushes out the air molecules as well as the complex of HC molecules. The air is only composed of 21.9% O2 molecules which is displaced by the HCs, still reading rich.
Remember that liquids change phase when going to the gaseous state and increase in volumn tremendously during that phase change, displacing the air/nitrogen. This is how the mixture reads rich when air/fuel passes out the exhaust valve during the critical scavenge cycle if EVC is a bit late for the head flows available. To compensate the exhaust valves could be recessed or sunk into the head a bit, allowing the fresh charge to pass over the almost closed exhaust valve.
Water when changing phase from liquid to steam expands 1,600 times. This phase change requires huge amounts of heat taken from the air when using water injection in an ICE, which elps control detonation. The huge expansion also aids cylinder pressure.