Good news, ass-havers! The answer is yes. Even better news is that the vast majority of what's likely to be expelled from your butt has potential to run a car, which is likely the best use for anything that comes out of any butt anywhere. So let's see how this ass-power works.
For the purposes of this article, I'll be focusing on two of the most common forms of ass ejecta, the famous two F's we all know and love: flatus and feces. From these two human exhaust products, there's two primary elements that can be harvested to use to run a car: methane (available in both flatus and feces) and hydrogen (available in flatus only).
Let's start with methane, since it's already in use in cars, though more commonly called natural gas. You can convert almost any internal-combustion car to run on natural gas, and there's several CNG (compressed natural gas) cars and trucks ready for sale today, from Chevy and Honda and a number of other auto makers.