2002 Mercedes Benz S500 water damage

My car took some water damage to the right side rear and front floor boards. This shorted out some computer and electric components which were replaced. Since I picked it up after having the new computer put in it, I have noticed the gas mileage is terrible. This morning on my way to work, about 11 miles, 10.5 is highway driving, my gas mileage was 8.2 mpg. I could see the gas gauge moving. Does this car's computer affect the fuel efficiency of the vehicle? What do you think is causing such poor gas mileage. I always use super unleaded.

Your thoughts are really appreciated.

Have a great day.

Mark Rodriguez