return line for EFI conversion

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R3dplanet

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I finally have everything assembled and gathered for my Megasquirt conversion. The car is a '65 Barracuda with a newly rebuilt 360. All of the Megasquirt circuit boards are soldered up and tested. I'm using a GM-style 670 throttle body newly purchased from Holley. All of the sensors (water, O2, vacuum sensor, MSD input) are already present. The throttle position sensor is part of the Holley throttle body. I also have a beautiful CNC'd adapter plate for my Weiand Stealth intake.

The only hardware I don't have is a fuel return line. Since this is throttle body injection, the fuel pressure is relatively low compared to multiport injection. I can see that I can purchase new fuel sending units that have barbs with my choice of 5/6" or 3/8" inlets and outlets.

Since the pressure is relatively low, I'm thinking that maybe 5/6" in and out would be alright, or perhaps 3/8" main and 5/6" return. I'm open to opinions on this.

What I'd like to see are photos or tricks of others who have added return lines to their tanks. I haven't done anything to the existing system and won't until I know exactly what needs to be done.

Thanks,
Marcus
 
I added my own return, and unfortunately, at the time I was thinking only of vapor return, to prevent vapor lock

I ran the car until the tank was quite low, then disconnected the front tube and allowed it to siphon into a can until the siphon "broke," IE the tank was essentially MT

I pulled the vent loose at the filler neck, and temporarily plumbed the 1/4" vent fitting out to "free air" with scrap tube and hose

I then got my MIG bottle (I use CO2 only) and plumbed the low pressure output into the fuel supply tube, allowing CO2 to flow into the tank, and pushing fumes out the vent which is essentially the top (filler neck) This tube, again, was extended out into "free air." I actually LIT this afire, so had a small candle like jet of flame, as the CO2 pushed the fumes out of the tank.

After several minutes, the flame went out. I then held a small torch near the tube opening, until no more flame of any kind would "try" to light off. I then knew that the entire tank was full of CO2

My Dart of course, is different than your Barracuda, on the Dart the front face of the tank is immediately behind the rear axle. I had cleaned off a spot on the tank, and after purging the tank with CO2, I took a sharp sheet metal awl and used a hammer to penetrate the tank, enlarging the hole with the awl to pass a piece of 1/4" tube. This was temporarily plugged at the end to prevent fumes/ CO2 from escaping.

Last, I simply silver brazed (hi temp silver solder) the 1/4" line into the tank. Now of course I wish I had installed a 5/16 or 3/8 fitting, because I'm running a Commander 950 injection system
 
There are many ways to plumb these.
I recommend a new 3/8 feed line and a 5/16 return.
For the return back to the tank you have a couple choices.
You can T into the filler vent tube but extreme caution must be taken to NOT cause any restriction for the vent or you will never get it filled at the pump.
I have found thin wall copper tubing T works good.

Another option is to log on to Summit or jegs and pick up a ready made filler hose return T.
Just cut the filler hose, insert the T and plumb the lines.
Clean and simple.

The pump is designed to push not lift or pull so it should be low and close to the tank.
The frame just ahead of the back tire works good.
Allways run a clear filter ahead of the pump. Fram G3 is 3/8.

I use universal steel prake lines for the new fuel lines. if needed, cut one end and remove the flare nuts and then double flare to help keep the hose in place under pressure.

Any restriction in the return increases the inlet pressure. This makes tuning a nightmare.
 

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Lookup my posts on this. 5/16" will work fine, but since you have a choice, use 3/8" for supply. All the new senders I have seen have a 1/4" emissions line. I used that for return in my 65 Dart, but measure 9 psi return pressure in the engine bay with my Walbro fuel pump (225 lph I recall). Next time I pull the sender I'll try flaring the 1/4" tube for less restriction.

In my 65 Newport, I drilled a hole for 5/16" return in the sender and rigged up pipe fittings w/ an O-ring seal. Never had a leak there. I measure <1 psi return pressure using a Holley Pro-jection 2D with their gear-rotor pump. Holley specs <4 psi return as I recall. I doubt the world ends if higher, as long as the pressure at the injectors is regulated correct. I run 22 psi there.

BTW, I put my EFI pumps on the engine bay frame rail and never had a problem. Maybe I'll starve the pump if I climb up a really steep hill in San Francisco, never tried.
 
Excellent information, everyone. I have a Walbro pump in my old fuel-injected 914 and it's a great pump. I'll order a sending unit with 3/8" output and 5/16" return, a good pump, regulator, filter, and some stainless brake line. I really like the idea of mounting the pump on the frame rail that Bill has in the photo.

When everything is ready I'll document the conversion and post it here.

Thanks, all.

-marcus
 
Unless referring to a specific Walbro pump...they are just another gerotor pump like most all EFI pumps. (GSL-392)
The only difference in all of them is the flow rate and the inlet and outlet fittings.

Nothing I know of makes them any better at lifting fuel.
Most electric EFI pumps are listed as being capable of lifting up to 12" above the fuel level.
Most tanks are about 12" deep from top to bottom.
So with that you really should not mount the pump above the tank.

If mounted at or below the bottom of the tank then it will always have a syphon feed to the pump just like when you stick a hose in the tank to syphon fuel.

There are lots of ways things can be installed and made to work.
But there are ways to install them to to ensure proper operation and long life.

Twisting wires together and wrapping in duct tape may work but it certainly doesn't last!!

If you do a quick google search you will find most installations that have the pump mounted forward still run the stock intank pump to feed the new one.
Ford used this 2 pump system on the F series trucks where they use a low pressure intank lift pump to feed the frame mounted E2000 EFI inline pump.
 
The TBI system operates on 13+-psi other than the 94-95 454 TBI which doubled the pressure and used smaller injectors for a little better atomization of the fuel.

IIRC that regulator is about 35psi.
The TBI has the regualtor built into the return side of the injectors in the throttle body.

"IF" someone was going to try and shortcut the install by not using a full return then the ford filter would be a better choice.

But...Having personally tried many of the shortcuts posted on the web over the last 10+ yrs for an EFI install, I can tell you that the chances of a vapor lock are greatly increased by not returning the unused fuel and vapor to the tank where the vented fuel cap can release it.



Here is the ford filter.Part Number: FF871DL
Alternate Part Number: FF871

But I don't recommend running without a return.


4
 
I put the Corvette filter/reg on my 65 Dart 273. The Wix one is $20 at O'Reilly's. I used for later MPFI. It regulates ~56 psi, too much for TBI or carb. I currently run a carb off the 9 psi return drop (plus in-line 5 psi reg). This regulator needs to be after the final pump, so if your pump is at the rear you can put the reg right after it and have a short return tube/hose to the tank, as inkjunkie says. That is simplist, but getting at the pump isn't fun, especially for problems on the road.

Running a single tube forward to the engine still follows Bill USN-1's recommendation to return "unused fuel and vapor" to the tank. It shouldn't cause a problem since EFI vehicles have done that since ~2001. I know Mopar Magnum engines started running a single tube then (reg in tank). I understand that was a federal mandate (return-less fuel) to lower emissions by avoiding heating the gas supply via a "to engine bay" loop.

The EFI pump in my Newport and Dart must be below the tank level, since when I test the flow from the supply tube, the gas pours out (maybe 1 gpm), much faster than the pump could flow. I don't think any public road or driveway could have a grade steep enough to starve my pump. I tried a pusher pump in the rear years ago, but it caused more problems than not.
 
Should the return line return fuel above or below the fuel level?
I would assume above to limit pressure losses in the return line.
 
It works either way.
I normally just return mine to wherever is convenient. But some recommend returning below the fuel like in most newer EFI tanks with intank pumps so there is less aireation and vapor as the fuel splashes back in the tank.
But as you pointed out, the higher fuel level the more back pressure on the return.
 
I have no problem installing a return line. Inline Tube has complete stainless fuel line sets and I'm happy to buy a pair of them.

One thing I'm having a hard time sourcing is good fuel sender with a 3/8" outlet and a 5/16" return. It looks as if 1/4" return is the norm. Reading on Megasquirt forums 5/16" return lines are much preferred, especially since Inline Tube doesn't make 1/4" fuel line sets for early A bodies.

I do have a Walbro GSL395 pump as of today, which looks to be perfect. It's rated at 15psi, and the throttle body has a built-in pressure regulator at 13psi. Nice low pressure.

Does anyone know where to get a fuel sending unit with 3/8" out and 5/16" return?

Thanks,
Marcus
 
Bear in mind that if a 1/4" fitting is the "best you can do" it will not be nearly as restrictive if you run 5/16 tube for the rest of the return, as it would be if you used all 1/4" tube. That, essentially, is what I have now..................

a homemade 1/4" fitting which was originally intended for vapor lock/ fuel return with a carb system, as I never foresaw an EFI on the car. If I recall, with the Holley TBI, I have about 2.5 LBS return line back pressure with 18 PSI operating pressure at the regulator.
 
Bill USN-1 said:
Unless referring to a specific Walbro pump...they are just another gerotor pump like most all EFI pumps. (GSL-392)
The only difference in all of them is the flow rate and the inlet and outlet fittings.

Nothing I know of makes them any better at lifting fuel.
Most electric EFI pumps are listed as being capable of lifting up to 12" above the fuel level.
Most tanks are about 12" deep from top to bottom.
So with that you really should not mount the pump above the tank.

If mounted at or below the bottom of the tank then it will always have a syphon feed to the pump just like when you stick a hose in the tank to syphon fuel.

There are lots of ways things can be installed and made to work.
But there are ways to install them to to ensure proper operation and long life.

Twisting wires together and wrapping in duct tape may work but it certainly doesn't last!!

If you do a quick google search you will find most installations that have the pump mounted forward still run the stock intank pump to feed the new one.
Ford used this 2 pump system on the F series trucks where they use a low pressure intank lift pump to feed the frame mounted E2000 EFI inline pump.
Click to expand...

Yes they do lift fuel better than the other pumps. I myself have called Walbro and talked to the Engineer that built that specific pump "GSL392". YES they have a special division just for that pump. I also emailed him pictures of my 3 pump GSL392 set up as I asked him the questions over the phone about the DEAD HEAD and Lifting Fuel. He says it has been tested to lift fuel up to 5 Feet. This is why it is used by the Diesel Truck guys quite often. It is also designed as a DEAD HEAD pump so if you have multiples like me you do not need to worry about fuel going right back to the tank through a pump that is not turned on.

View attachment phpmyA57TPM.jpg
 
That right there is wicked cool.

Lucky for me I just need 13psi for my run of the mill TBI project.

Still though. Very, very neat.
 
Mad, that's good to know. Do you have any other specific info on those pumps, numbers, volume, pressure, etc? Holley "would like to get" about 3x the price for those same pumps.
 
67Dart273 said:
Mad, that's good to know. Do you have any other specific info on those pumps, numbers, volume, pressure, etc? Holley "would like to get" about 3x the price for those same pumps.
Click to expand...

Here is a link with some info and a Video.... These little pumps will support 600-650HP Each. They are super quiet too. With all 3 of mine on at the same time you can barely hear them.

I am using an Aeromotive Boost referenced regulator. Psi at the rail is set to 45Psi and boost referenced from there so I should have more than enough fuel for my application even if I lost a pump. There is also 2 safety features I have set up in my mega squirt MSX3. 1 is the Lambda safety feature, the other is a fuel pressure safety switch that is in 1 of the ports on the regulator and wired to the mega squirt.

http://www.gsl392.com/
 
Thanks. I don't have "the numbers" but that is the same style pump I have on my Holley Commander 950, not the original pump.
 
67Dart273 said:
Thanks. I don't have "the numbers" but that is the same style pump I have on my Holley Commander 950, not the original pump.
Click to expand...

I had a Holly Commander 950 on my sand car that had a North Star engine in it. It worked flawless for the 6 years I had that car. From NA to a Vortec Supercharger at 10psi, it never missed a beat.
 
Mad Dart said:
Yes they do lift fuel better than the other pumps. I myself have called Walbro and talked to the Engineer that built that specific pump "GSL392". YES they have a special division just for that pump. I also emailed him pictures of my 3 pump GSL392 set up as I asked him the questions over the phone about the DEAD HEAD and Lifting Fuel. He says it has been tested to lift fuel up to 5 Feet. This is why it is used by the Diesel Truck guys quite often. It is also designed as a DEAD HEAD pump so if you have multiples like me you do not need to worry about fuel going right back to the tank through a pump that is not turned on.
Click to expand...


OK you win...
LOL
Other than the specific flow rate of each inline pump, everything you describe with that pump applies to all inline "EFI" pumps.
The pump is fine. It works and the prices are coming down on it now that there are so many others on the market.
You can do a quick search for some others like the E8228, E8445, E8120, E2000, E2182.
Same basic set up with variations in max pressure or flow rates and fittings.
The walbro is nice with the standard 10mmx1 threads for other fittings.

For stock applications the simple E2000 on ebay for about $25 works fine.
You just match the pump the the application.
 
You can get a new Walbro pump ~$100 w/ mounting kit on ebay. I recall 255 lph, but even the 195 lph would work for me. I have won new ones cheaper and used ones ~$40. As Bill_USN-1 says, there are many different fittings available that screw into the 10mm threaded ports. Most people use the 5/16" or 3/8" hose barbs. I have 2 big alum (blue) AN fittings that came on one pump. You can find those on ebay, or PM me since I'll never use. If you prefer, you can buy the same Walbro pump > $200 with logo from Holley, MSD, ... The other external EFI pumps I know of are either 5/16" hose only (Ford truck type) or strange fittings (Bosch for M-B, BMW, 1/2" tube suction, banjo w/ check valve outlet, and big body).
 
Check this out. I just saw this post about using a big NAPA spin on fuel filter as a surge tank. Plumb it on a remote filter manifold from the mechanical pump on the motor. Yes, the mechanical pump, then you run the EFI pump out of that filter and plumb the return line through a T that feeds the surge tank and returns to the rear tank. That way you only need to run max 2 feet of high pressure EFI line and the rest you can run 5/16 nylon 80's Ford nylon flexible fuel line to push on fittings. This also reduces the chance that if you uncover the sock if you run it low and take a corner, youll aerating your hi pressure line and leaning out your motor. This surge tank will burp any air before the HP pump gets it AND provide a pretty good filter too. Could help...
acc-short-and-long%20web.jpg

Thanks to B.C Broncos web page.
 
Marcus,
I'm installing the GM TBI on my 66 Barracuda and I just modified my sender for a 5/16 return and will use the 5/16 for supply as well. I was going to put the pump in the tank but changed my mind. Check the thread below and look for the latest post for a photo with my sending unit.

http://www.earlyabodyforum.com/board/messages/2/9253.html?1358804677

spankmeister7 said:
I finally have everything assembled and gathered for my Megasquirt conversion. The car is a '65 Barracuda with a newly rebuilt 360. All of the Megasquirt circuit boards are soldered up and tested. I'm using a GM-style 670 throttle body newly purchased from Holley. All of the sensors (water, O2, vacuum sensor, MSD input) are already present. The throttle position sensor is part of the Holley throttle body. I also have a beautiful CNC'd adapter plate for my Weiand Stealth intake.

The only hardware I don't have is a fuel return line. Since this is throttle body injection, the fuel pressure is relatively low compared to multiport injection. I can see that I can purchase new fuel sending units that have barbs with my choice of 5/6" or 3/8" inlets and outlets.

Since the pressure is relatively low, I'm thinking that maybe 5/6" in and out would be alright, or perhaps 3/8" main and 5/6" return. I'm open to opinions on this.

What I'd like to see are photos or tricks of others who have added return lines to their tanks. I haven't done anything to the existing system and won't until I know exactly what needs to be done.

Thanks,
Marcus
Click to expand...
 
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