I don't have data for the bus engine, but for the plane engine a 35 degree increase in air temperature equates to a 5% loss of power, but a reduction in fuel flow.

The point here is that on very cold days the bus will produce more power, and there will be an increase in fuel flow adversely affecting mileage. If the charge air is overheated power will be down, but to maintain a given speed compared to cold temperatures fuel flow should be less, increasing mileage.

That is on a plane with mechanical power adjustments. I don't know if the DDEC on the bus adjusts fuel flow to compensate for charge air temperature. The black smoke may be an indication that fuel flow is a function of the throttle position only, although I was under the impression there was some compensation for turbo boost.

I'll be interested in hearing Jack's opinion on the fix and its impact, also what has changed on Roger's coach causing the black smoke. If there is no temperature compensation in the fuel flow then Roger's issue may just be that the warm temps are not providing sufficient charge air density to burn all the fuel under throttle inputs. So far we have had a relatively cool summer.