Returnless Fuel System?

[Whirlwind]

Can anyone explain the parts involved in the returnless fuel system and how they differ from the return fuel system? How crucial is keeping the fuel system 'returnless' and how feasable is converting the returnless to the return style? It seems like the returnless fuel system causes more problems than solves..

[pgtatx]

Returnless fuel system is basically made up of a single fuel rail, single fuel line, and a Smart fuel pump (as they are called), pressure is controlled by the pump itself.

The Return system is made up of a different fuel rail...almost like a U shape with one fuel line in and one fuel line that returns back to the tank. Inline with the fuel line is a Fuel Pressure Regulator, which does what it's name says, and there is a standard fuel pump that basically just keeps pumping.

The ECU calibrations in the 2 cars are different...the ECU controls the pump in the returnless system.

To do a swap, you'd need the fuel rails, FPR, ECU, and fuel pump from a return car, and then you'll need to route a return line back to the tank...you may want a tank from a return car too if they happen to be different.

That's basically all...

[Whirlwind]

thanks! I keep hearing the terms tossed about and was left wondering if there was something more sinister. I can tell it isn't. I am guess that the reason for the second (return) fuel line is for fuel pressure overflow in the event the fuel pump sends too much fuel to the engine.

[pgtatx]

Right...the smart pump is supposed to pump only the fuel needed.

Another thing about the return system had to do with a cooling factor of the fuel when pumped out of the tank, through the rails and back into the tank. The fuel would cool and be put back into the tank again. I was told this by a Mazda engineer, so I assume it is true. Don't know it's tru purpose though.

[BigBlueWienke]

which is better to have for performance/upgrades?