<  This catalyst causes a reaction on it's
>  surface which converts nasties (oxides of nitrogen as monoxides of
carbon,
> etc)
>  to their fully oxidized (and less harmful) states.  >>
>
>
> So then why would it be a factor in fuel economy? Being that it is in the
> exhaust, the fuel burned by the van would be used before that.

The O2 sensor sends feed back to the ECU which then adjusts the amount of
fuel delivered by the injectors...

Bill