fuel systems

What is the difference between return and returnless fuel systems?

A return fuel system is like a loop. Fuel is pumped from the tank into the fuel rail, and from their it takes one of two routes: it either goes through the injectors, or into the return line and back into the gas tank to try again. Fuel pressure, and ultimately the amount delivered, is controlled by placing a restriction on the return side of the fuel system (fuel pressure regulator), more restriction means more pressure, and more pressure means more fuel will move through the injectors. Plus side is the ability to use a rising rate fuel pressure regulator. A returnless system has no return line (hence the name).

thanks for your answer. also BTW on the returnless where is the fule presure regulator? before the fuel rail?

Yep, the fuel pressure regulator is in the tank.

cool thanks for the info.