For twenty years my fuel filter has always stayed full. Recently it has not. I have decided the fuel pump which is twenty years old is not functionally correctly. I also am concerned with trash and/or debris in my gas tank simply because I have had the truck for over 38 years and have never cleaned the gas tank. I seems to make sense that in that period of time there would be a possibility of trash getting in to the tank and possibly restricting fuel flow to the engine.
