You need to replace your fuel filter because it becomes dirty and clogged with small contaminants over time. The purpose of your fuel filter is to trap and remove these contaminants from the fuel so they do not enter your engine. As the filter traps more and more debris, it starts to become clogged. Once it is clogged, it will not allow fuel to pass through properly. This is why you must replace the filter with a new one at regular intervals.