A returnless-type fuel system is one that is designed to use the powertrain control module (PCM) to regulate fuel delivery. A fuel pressure sensor mounted to the supply rail of the fuel injectors allows the powertrain control module to keep an eye on the fuel pressure.

What is the difference between a return fuel system and a Returnless fuel system?

A return style fuel system does it mechanically with use of a fuel pressure regulator. Typically, pumps are run at maximum voltage supplying as much fuel as they can. The FPR then returns excessive fuel back to the tank. A returnless fuel system does it electronically with a FRPS and FPDM.

How does Ford Returnless fuel system work?

With an electronic returnless system, the PCM can now raise or lower fuel pressure at will. This system consists of a rotary vane fuel pump (same as before), fuel line (pressure only), fuel rail pressure sensor (that also contains a temperature sensor), fuel pump control module and, of course, the PCM.