plumbing aux tank into main tank

[pro253]

hay guys as the title sugests am trying to work out hooking my aux tank so all i have too do is hit a switch for an electric fuel pump to fill main tank from the reserve whenthe main tank gets down low , my car is a efi 4.2 so am looking at wats the best way to fill the main tank ie inlet from reseve, was thinkin but unsure on this because its efi but was thinkin (havent acct looked under the car as of yet) maybe i could runa y piece into the return line back into the main tank then all i have to do is plumb up a fuel pump and line but was also thinkin would this create a problem with the fuel pressure ??? how much pressure is on the return line ??? whats anyones thoughts as would realy like too hook up this aux tank for a longer range, the pump i was going to run to feed the main off the reserve was just something simple like a holley red or blue which i have not too worried about the noise of them as its not going to be on constantly just till it empties the reserve. Cheers John

[JDGQ]

there isn't huge amounts of pressure in the return line from the engine so i guess you could put a T piece in the return line and like you said just pump it to the main tank that way.
You'd probably want to put a one way valve in the line leading to the sub tank thou to stop the risk of over filling the sub-tank when not transfering fuel.
My only thought is whether if the lift pump flows more then the fuel line can carry would it create a back pressure problem for the fuel rail?
Then the other way being if the pump can't provide sufficient pressure would it be able to pump out with the small amount of pressure in the return line?
I may be over complicating things and over thinking things.

[Wozza244]

If you have a sub tank sitting at the same level as your main, you will need a transfer pump. And also make sure your breather works.
My sub tank sits above my main, so i have it gravity feeding into the main via T piece into the filler neck return.