O2 Sensor Open/Close Loop

[RABBITT_Andrew at mv8.orbeng.com.au]

>My ECM is in closed loop mode at idle and part throttle. At wide open
>throttle is goes into open loop mode ( it stops reading the O2 sensor 
>
>
>WHY?
>

The reason that closed-loop A/F ratio control was introduced was 
almost entirely emissions control related.  Three-way catalytic 
conversion only operates in an extremely narrow A/F window.  This is 
because you are oxidising HC and CO (so you need excess O2 or another 
oxidising agent) and reducing NOx (so you need a reducing agent) 
simultaneously.  

The only point where you can get this to happen is at stoich A/F, or 
more correctly by perturbating the A/F around stoich.

When you go to WOT, no one seems to care how much junk comes out of 
the exhaust, therefore emissions control is thrown out the window and 
the calibration goes rich for best power.  You never see WOT in a 
emissions drive cycle (to date), therefore it doesn't impact on the 
emissions certification.

I think you'll be hard-pressed to find a production car with a EGO but 
no TWC, they go hand in hand.  It has next to nothing to do with fuel 
consumption since you want to go lean to improve this.

Andrew Rabbitt