I've been watching gallons per hour, which has never gone down to zero... There are a few other things I can see such as throttle position or ignition timing. I've never seen any indication it's actually stopping fuel flow / closing the throttle / stopping the ignition. Also, my engine is a very poor brake - it seems more likely to rev up then slow the car down on any significant hill, which I'd think could be another sign it's still powered.