It's a given that narrowband O2 sensor (Lambda) output swings up and down within the 0-0.9v range, but everywhere (on the 'net including here) I am seeing people say this is due to the ECU in closed loop in effect firing the injectors rich/lean trying to maintain stochiometric mixture but overshooting to some extent.
Whilst this may be true in many cases, I am aware that in other cases it is not. I know this because I have monitored a narrowband sensor on a carbureted V8 (no ECU at all) and it also displays this behaviour.
The frequency follows engine rpm and rises to many times per second.
Does anyone know why?