It affects the O2 sensor, which affects your mixture.  The
O2 sensor is (as was mentioned) in the cat on the 2.1

Keith

"Paul M. Hillbish" wrote:
>
> In a message dated 1/22/01 10:36:40 AM Eastern Standard Time,
> keith_adams@transcanada.com writes:
>
> <<  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.
>
> --Paul--