I know this has probably been talked about before, so any direction is helpful.

1993 Ford F-150, 4.9L I-6, EFI with dual tanks.

I am converting to a dual Weber setup from Clifford Performance. We have managed to get the fuel pressure under control but are having trouble with the return circuit. Since I have dual tanks, the switch selects which pump and return the fuel goes to. With the carb conversion alot of wiring has been simplified including how the return knows which check valve to open to allow fuel to return. If I delete the check valves, there is a danger that a tank can be overfilled.
I am converting to dual Webers to eliminate the head cracking problem that occurs because of poor fuel/air distribution in the intake system of the 4.9L. A problem that apparently plagues all of these engines.

The engine runs like a top using Clifford Performance's recipe for a torque monster 6 cylinder! (Clifford Performance - 6=8 Clifford Performance Intakes & Headers) (Shout out to Larry and his team!)

We just need to figure out how to be able to use both tanks without getting too complicated. Eventually, if I have to change the entire fuel system (selection/pump/return and all), I'll do it. Right now, I'm trying to get my project driveable again, so I can do the suspension and steering upgrades.

Any help and/or direction is appreciated

 

Why bother with the fuel return?
Where is the fuel return connected to?
Fuel pump goes to fuel regulater then carbs. There is no return.

What does Clifford Performance say about a return?

 

A fuel return is needed for the excess pressure of the high pressure EFI submerged pump.

The return is connected to one side of the regulator and the other end to the submerged pump. This circuit contains a check valve that prevents fuel from returning to the wrong tank and overfills.

Yes, there is a fuel return. Look at the fuel schematics for the EFI.

Clifford Performance says there is a return and if I want to use dual tanks, I need to figure something out or use a different tank/pump/selector setup from an older, non-EFI truck.

 

Why are you converting to carburetors? There is no air/fuel distribution problem in an injected 300/4.9L because there is a fuel injector at each cylinder spaying fuel directly at the back of the intake valve. It is a dry intake manifold. I have driven both carbureted and EFI 300s. You aren’t going to convince me that a carburetor is better. EFI solved the fuel distribution problem of the center cylinders running rich while the end cylinders were lean because the fuel fell out of suspension.

If you are still using the dash mounted switch to control the individual pumps, I am not following your thought process about the check valves in the fuel delivery module ( pump assembly). Yes. There are dozens of threads about the check valves going bad causing all kinds of cross-flow problems including a tanks to overflow.

I would direct you to put it back to the way it was and send the carburetor kit back to Clifford. The picture they use for the 300 ad is a carbureted truck from the factory.

Yep. He was aware of how the OEM system works. I’m thinking the statement from wwhite was directed at where you connect the fuel return to the carburetor. That carburetor has a fuel return port?

 

The check valves inside each Fuel Delivery Module (FDM) are activated by which pump/FDM is selected. The running pump will unseat the high pressure check valve so fuel flows to the engine. On the return side the selected pump also triggers the shuttle valve to open so fuel returns only to the selected/running pump assembly. The unselected FDM's check valve and shuttle valve will be closed.

Fuel Delivery Module (FDM)


If fuel is getting into the unselected tank then you have a bad check or shuttle valve in the that tank. This crossflow issue plagues this vintage trucks.

 

x2 Probably just easier to replace the FDM and get the return system working right than ripping out all the EFI to go carb. JMO.

 

You do not have EFI, so all the information about EFI is irrelevant to me.

If your fuel pumps are working correctly in both tanks, and you haven't messed with the factory fuel lines, switch and return, just connect the return to your regulator. Same way you connected the fuel line from tanks, to regulator.
There is only one return line from the EFI manifold.

 

In the electrical schematic there is nothing to do with fuel return, unless I'm looking at the wrong diagram.

WIth the fuel plumbing, looks like there should not be any issues you describe:

 

I agree when using a regulator that is designed to bypass the excess fuel back to the tank, just like the EFI setup, there should be no issues with using the stock fuel system as-is. If you are getting crossflow then fix the problematic FDM.

 

Thank you all for your input.

My4Fordtrucks: I have no intention of putting it back the way it was.

When I get the truck back, I will follow all the steps prescribed by the knowledgeable folks of this thread. Thank you for the input. Please don't hesitate to respond if something comes to mind. After the fuel system is finished, I will let everyone know what solution we came up with.

 

Another solution would be to add another regulator. Each pump gets regulated to 7psi (or whatever), before they T together. Check valve prevents backflow, excess from each regulator is returned to that pump's tank.

This way, you can delete the return line from the engine, keep your factory wiring, and all's right with the world.

 

There's something I had not considered. I'll give it some thought.

I need to study all the schematics and see what can be done. I'm sure I'm overthinking this.

 

What are your plans for controlling power to the pumps? Right now they're controlled by the ECM. However, once you pull the TFI distributor out and replace with whatever you're going to use for the carb setup, there will no longer be a pip signal present for the ECM to sense engine rotation with and it won't send power to the pumps.

If you want to continue using electric pumps, you're going to have to graft in a control system like the '87 351/460 trucks used that used the oil pressure sensor and a bunch of relays to control the electric fuel pumps.

Converting EFI to carb is a never ending series of headaches. Then once you get it running it's a never ending series of headaches chasing driveability/tuning issues with the carb. Some people just love to fiddle with carbs though, so more power to you if that's you!

 

Actually, I may have found a solution to the power problem for the pumps. One gentleman used a keyed power source to send power to the tank switch which selectively activates the pumps. It seems to have solved his problems.

The carbs I'm using are Webers. Now before anyone gets excited, I know a Weber can be frustrating for the uninitiated and uneducated to setup. Fortunately, the shop I'm working with set them up on a flow bench. They matched my engine parameters, intake, cam, and exhaust setup and they came ready to run with minor tweaking. Also, I have been doing some research on the Weber and they seem to be remarkably simple. Most setup problems appear to be owner induced (trying to make it work when it's outside the parameters for the jets installed).

All that being said, I am bound and determined to make The Turd (as my wife affectionately calls it) a living thing of beauty.

I will keep everyone posted.

 

I have a '94 extended cab that originally had a 5.0 fuel injected...when I bought it the previous owner had swapped for a '96 5.8 police package and had stripped the fuel injection and 4bbl carb...but they had removed the back fuel pump and had a small inline pump just running from the rear tank...I bought another rear in-tank pump and took it apart... I removed the pump motor from the assembly and replaced it with a longer line to the bottom of the assembly....did the same on the front tank...then bought a 20-35 gph inline pump (hard to find at that gph) and bought a 12 volt actuator wired to a toggle switch next to the fuel pump switch on the dash...there are four wires to each of the tank pumps,two are for the sending unit and two are for the pumps that were removed from the assembly...I also unplugged the tank wires fron the back of the fuel tank selector switch on the dash....and finally we cut out parts of the fuel lines that weren't needed including the fuel return and replaced those sections with rubber lines....and a fuel pressure regulator on the firewall with a return fuel line to the front tank....if I stay outta the 4bbl I get 18 mpg easy on 89 octane.... I know it's a lot of reading but my son and I did all this on a Saturday....hope this helps...good luck