Fuel return line using 71 ECS system?

I have a 72 Cuda with the 71 style ECS "seperator".
I am installing a Fi Tech fuel system and planned to use the 1/4" {EDIT} vent line to the vapor seperator but if the canistor was meant to catch the vapors and the carb used them, without the canister then I wont really be vented at all will I ?

You could possibly vent through the cap or some other way

Also be aware that some EFI systems want the supply and return lines to be the same size so you might want to to check with FI tech on that.

When using the Fi Tech Command center no return line is required.

The issue I think I'm going to have is that the vent line these cars had was meant to run to the vapor canister. Now hooking that same line to the Fi Tech because the unit needs to be vented back to the tank, there is no vent now.

The 3549088 Fuel cap is not a vented cap, Right? It just relieves vacuum. Anyone have a good PN for a vented cap to replace this one?

The fuel return line should go right back to the fuel pickup and dump the fuel in the tank. Fuel pickups with 1/4" return line are readily available.

The ECS system does make a great tank vent setup. Much better than a vented fuel cap which can hold quite a bit of pressure or vacuum before venting.

As far as the rest of the system, what does it look like? If you are thinking of a frame mounted high pressure pump be careful. High pressure pumps do not like to suck. Noise and early failure follow. In tank pump or one of the sump systems fed by a low pressure pump are much better.

Ooops I meant it's a vent line not a return line, no return line is required for the set up I am using, and the previous posts above show the Command center type pump I am using. It has it's own sump fed by the OE style factory fuel pump.

Sounds good... and please update when you get her running. That is a slick setup.

That said, there is still possibility of vapor lock on the suction side of the stock style fuel pump. A return line on the outlet side of the low pressure pump could help keep the fuel cool... that is the idea with the 3 prong OE fuel filter. The return is through an orifice of about .050" to maintain adequate flow and pressure.

I see what your saying. As the factory unit was a sealed setup with the charcoal canister and the tank vent line vented to the charcoal canister. But the unit you are using has to be vented to the gas tank so you plan to use the original vent line to the canister to go to your new units vent to the tank. And you need to have the factory tank vented of course. They make vented caps that are vented at all times or at least they use to. The newer caps as stated will vent at a certain vacum or pressure release but are made as to only vent under enough vacum or pressure before it gets to much to damage the tank. Are you planing to use the factory vapor seperator setup ? Course if you dont you could plug them vent lines to it and use one for the tank vent and then run a tank vent line from it. Or if you can get a normal fully vented cap you can use it as my 63 uses a vented cap as the tank itself has no vent line from it or from the filler neck. When I lost my cap and could not find the one I needed right away I put a small slit in a pressure/vacum cap rubber gasket so my tank would vent all the time until I got the right cap. Course with any vented tank you may get fuel smell in the garage on hot summer days unless you you use a canister vent setup. Good luck with it.

I take it that setup takes the 5 or 6 psi from the stock fuel pump and ups it at that unit for the fuel injection setup ? What fuel pressure does that setup run at ? Ron

Thanks guys, Ron a few excerts from some Fi Tech instructions:

"The Fuel Command Center contains an internal float mechanism that shuts off the fuel flow once the sump tank is filled.A 340 L/PH EFI pump is submerged in the fuel in the Command Center sump tank. The Center also has a regulator and fuel pressure gauges."

FiTech offers two different fuel delivery options. One is the 40003 Fuel Command Center. When using this option, you can configure the system to operate on a returnless basis.

Remember that your system will be running at 58 PSI so consult a professional if you are not certain about this portion of your installation

ahy, in another post (about vented caps as the system calls for one) we ended up back on these topics, and I asked for the 71 service manual info on the exact return/venting and ECS set up to help. Here is something I was emailed and am considering if I can tap it into my return from the Command center vent. Returned Command center fuel would only be able to get to the ingoing low pressure fuel line sooooooo that could work

So I will run an ESC line from the factory fuel vapor seperator in the trunk to the engine (used to go the the charcoal caniser first), and a return/"vent" line from the Command center to the fuel sending unit

Also I have a post in the project/survivor section on this car and all my upgrades if you want to see how it goes

This is the exact reason I went with a Specta FI tank instead of the Command Center.
The advertising is a little deceptive, because you still need to run "vent" line back to the tank.
So whether you call it a return line or vent, a line is needed.

FI tank is only $250, CC is $400

Thanks for the info "Ucudant" as I had not seen that system before and was curious about it. Good luck with your hook up. Ron

No problem Ron.

cnxt I looked at the Specta EFI tank and went this route to prevent running lines... that didn't go as planned I wanted to be able to convert back to stock as easily as possible while swapping any peformance parts generically to another mopar. Plus these items were designed to work together. I can always change/upgrade any EFI parts later though too.

How do you like your system?

I am questioning the level at which my return would be. They state it needs to be above the fuel level. Do I need to T it into a line as it enters the fuel vapor seperator rather than the return nipple at the fuel sending unit?

For the vent only, the OE canister in the tank should work fine. Challenger1 (Gary) posted a good diagram of the vapor separator in the tank. You should be able to search for it. Once you find it, I think you will have a good idea on how to set it up. I use that as vent for my EFI challenger. Originally, the "atmosphere" vent for the vapor separator went to the engine. I simply ran it inside the rear frame rail which is where earlier year vents ran.

As far as using the existing return line as "vent" for your sump I am not sure. It may work OK with the small amount of fuel flowing from the 3 prong filter.

You know just something to keep in mind but the factory vapor return line from the 3 nipple filter/vapor seperator that the factory uses should have a pressure relief valve at the tank or in that line near the tank I believe as it is there to hold a small pressure in the vapor return line so that setup would not let the fuel in the line and filter/vapor sep drain back into the tank and let the fuel line run dry when shut off. I believe the info on it is in some year service manuals as I just remember that and thought you should know. Ron

Ok newest idea:

The tanks going to be vented via the fwd most line from the fuel vapor seperator fwd to the engine.


I think I can take the return "vent" from the Command center and T it into the line shown. Thoughts?

That is the same as what I suggested earlier, only I said T it in up front.

Like I said earlier, vent the pump sump/comand center to the vent line at the valve cover breather. Tee it in there, why run it all the way to the rear when the factory vent line ends at the valve cover breather?

Mount the sump as low as you can up front.

Because it's not a true "vent"... it will return raw fuel

I'm thinking I can return the "vent" to the rear most line of the liquid vapor seperator as it appears to sit the lowest and is the units fuel return line. Thoughts?

That makes sense to me.