MFI Return Fuel Tee

[50/50]

The diagram for the MFI fuel system shows a Tee which splits to the pump and to the tank. Is the Tee a simple flow through or does it have any type of
back low prevention?
Thanks,
50/50

[edmayo]

Just a simple 'ol' piece of tubing here, with nothing up its sleeve!

[Grady Clay]

It depends which ‘Tee’ and the year.

With the 1969 E&S and the ’70 T,E,S, the front-mounted electric fuel pump has a simple ‘Tee’ returning fuel from the pressure relief at the pump and the return fuel through the center (pressure regulating) fitting at the fuel filter console.
This returns the combined fuel to the banjo fitting at the gas tank drain plug.

Beginning with ’71 models, the electric pump was moved to the rear and the ‘Tee’ was a hose assembly.

Sometime later (perhaps during the ’73 model year?), Porsche added a ‘restrictor’ in the part of the ‘Tee’ returning fuel from the fuel filter console.
According to the late Warren Hall, Jr., “The restrictor is pill-shaped, approx. 7.5 mm OD and 10 mm long, with a drilled hole 1 mm in diameter in the center, with slightly rounded ends.”
My memory agrees with Warren’s measurement.
This 'pill-shaped' restrictor was inside the hose (not the metal 'Tee' pipe) returning fuel from the fuel filter concole.
This certainly would dramatically reduce the circulating fuel at idle but probably raise the fuel pressure at the piston inlets in the MFI pump.


I suspect this was done to cover some marginal situation with high fuel temperature, lower vapor-pressure gasoline.
I prefer higher circulating flow to keep the MFI pump and filter cooler.

Best,
Grady