[Fat Charlie]

It may simply be to throw enough BTUs down the exhaust pipe to keep the cat running. Look back here:

http://ecomodder.com/forum/showthrea...ing-20338.html

My car failed CA emissions testing recently, and I'm confident my hypermiling had a direct relationship to the problem.

The failure was because some of the drive cycle monitor readiness flags hadn't been set since I cleared the check engine light/malfunction indicator light in October. Since then, I'd driven 800 miles, but the catalytic converter driving cycle is 15 minutes at speeds between 60-100 kph, and I hadn't done that in 4 months.

The next day, I warmed the car up, driving it enough to add 100 miles since the test failure. The car passed smog testing. Examination of the retest shows cleaner emissions after driving the car a distance at speed.

I drove the car 900 miles RT to/from SoCal last week, and the cat stayed lit, between 1101-1185 degrees F. When I do my normal low speed P&G, cat temps are 285-550 degrees F, too low to light the cat.