They get dirty from crap in the fuel.
But if you don't fix your FPR problem it won't matter what kind of injectors you have in there. The ECU ajusts the a/f by ajusting the amount of time each injector is open. It wants a constant pressure difference between the fuel and air intering the cylinder. If that pressure difference begins to drop, less fuel will make it into the cylinder and you will run dangerously lean like you are now.
But if you don't fix your FPR problem it won't matter what kind of injectors you have in there. The ECU ajusts the a/f by ajusting the amount of time each injector is open. It wants a constant pressure difference between the fuel and air intering the cylinder. If that pressure difference begins to drop, less fuel will make it into the cylinder and you will run dangerously lean like you are now.