Roger wrote:

You will find that many of our engines run rich to keep the combustion
temperature low and then have to pump air into the catalytic converter
so the excess can be burned.

I hope not :-)) That would be a sure way to burn out your catalyst.

Gasoline engines do run rich however at high load conditions, which are
not met during emission cycles. But the excess fuel turns into CO
instead of CO2 (thus burning more fuel with less O2) or even goes down
the exhaust pipe unburnt. Noone cares, at it will never be measured.
This is one of several reasons, why the ongoing tightening of emission
standards has become a joke by now.

The only conditions, when so called scondary air is pumped into the
(rich) exhaust is at fairly light loads during warmup. This is done to
get the catalyst to its operating temperature range more qickly.

At least a good portion of the reason for poorer mileage over here is
due to some specific anti-pollution measure.

There is a slight influence, but it's not a big deal.

regards,
Friedrich

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