EFI Return Line Size

[Ronno6]

I have purchased a Fitech TBI fuel injection system for my 84 C-10
with a 1995 350.
The EFI will use their Force Fuel system, a tank fed by the engine's mechanical fuel pump. The tank has an integral HP to feed the TBI.

Fitech recommends a 3/8" return line, but says that a 5/16" will suffice.
The stock pump/system uses a 1/4" line.....

I can't see why that won't still work, as the only returning fuel is from the Force Fuel tank being
filled by the OEM pump........

I have a dual tank system with the selector valve, which has 1/4" fittings. So using larger return to the valve will not really make a difference......

Anyone have experience with this system??
How did you handle the return line?

 

[Ricko1966]

Boy I can't
see why that wouldn't work either,the guys that designed that just must not know what they are doing. I'd suggest you just do it any way you thinks good. Heck I wouldn't even even try talking to them about my specific situation,why they recommend that and what the possible cause and effect is.

 

[Ronno6]

I'm not even sure why a return line from the Force Fuel tank is necessary with the return line from the mechanical pump.....

 

[Ricko1966]

I'm going to go out on a limb here,and say their tank is probably a reservoir. They are using your original pump to fill their reservoir. There is a second pump of their specification in the reservoir providing fuel at a different pressure and volume than your factory pump. No or insufficient fuel return will cause an increase in fuel pressure. I make bypass regulators that work on that principal,the more fuel fuel I flow through the restriction in my return line,the less fuel pressure I have.The less fuel I let flow through the restrictor the higher my fuel pressure,running 1/4 return instead of 3/8s as the manufacturer recommends,I have no idea what effect it will have on pressure.No return I have no idea what the dead head pressure of their pump is. I'd bet the guys that designed the system would know this stuff

 

[bucket]

I'm going to go out on a limb here,and say their tank is probably a reservoir. They are using your original pump to fill their reservoir. There is a second pump of their specification in the reservoir providing fuel at a different pressure and volume than your factory pump. No or insufficient fuel return will cause an increase in fuel pressure. I make bypass regulators that work on that principal,the more fuel fuel I flow through the restriction in my return line,the less fuel pressure I have.The less fuel I let flow through the restrictor the higher my fuel pressure,running 1/4 return instead of 3/8s as the manufacturer recommends,I have no idea what effect it will have on pressure.No return I have no idea what the dead head pressure of their pump is. I'd bet the guys that designed the system would know this stuff

I wonder if their return is biased more towards the truck tank, rather than the surge tank? If rail pressure returns to the surge tank, then it should just constantly recycle to the rail and the stock return line wouldn't see any additional flow. Assuming there's some type of float valve in the surge tank so the stock mechanical pump can maintain the proper level.

 

[Ricko1966]

I wonder if their return is biased more towards the truck tank, rather than the surge tank? If rail pressure returns to the surge tank, then it should just constantly recycle to the rail and the stock return line wouldn't see any additional flow. Assuming there's some type of float valve in the surge tank so the stock mechanical pump can maintain the proper level.

I would assume excess fuel is being returned to the truck tank,not the surge tank, I very well could be wrong, I am making assumptions based on other things I have seen and worked on.

 

[hogdaddy]

I was curious about your setup. Here is their video.
If you drop your tank and drain fill with water, you could drill safely for the return bung.
Then run the correct size line.
Besides, they advise not to have the return on top of pick-up.

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[Ricko1966]

You don't even have to drain and fill with water, stick a garden hose in a tail pipe and in the tank with an engine running. The exhaust gas will displace the gas fumes there is no oxygen or fuel in exhaust fumes,no oxygen and no fuel means no reaction to heat or flame.

 

[hogdaddy]

I believe you still need access to the top of tank to install the bung.

 

[Ricko1966]

I believe you still need access to the top of tank to install the bung.

Oh yeah,and dropping a square tank is freaking easy. I was just stating that exhaust gas can be used as an inert gas when doing gas tankrepairs/mods.

 

[Ronno6]

Upon re-reading their installation instructions, no requirement is stated regarding return line size. Dunno where my thoughts on that came from. I tend to retain information that I come across, but can not return to when needed.

Anyway, as I said that I have dual tanks and a selector valve, installing return bungs in both tanks is not an option, as the selector valve returns fuel to the selected tank, and that return connections on that valve, as well as the return lines from the valve to the tanks are 1/4"....

As the EFI system does not add any fuel to the equation, the 1/4" line should suffice as it worked in the original system.
I still think that I can cap off the return outlet at the mechanical pump.

Yes, the Force Fuel tank IS a reservoir in which the HP pump resides.