Hi Shawn,

I'm unclear and interested in knowing more as well.

I read somewhere (sorry, can't remember if the source was reliable) that the equivalence ratio is used in the feedback strategy to allow for transient conditions while still remaining in closed loop, like heavy acceleration/deceleration, unusual coolant or intake air temperatures, etc. If that's correct, it seems to me that an A/F sensor would be more useful, but I believe that I've also seen that in the data stream of a conventional HO2S system.

Additions and/or corrections are invited.

Sincerely,

Michael Barry
Technician
Quick Stop Smog & More
Sacramento, California, USA