Care to speculate on tbi fuel system plumbing?

**Overland** · 10-19-2022

I'm surprised to find that a drop in sending unit for the original tank is not common, nor does it even appear to be available in the aftermarket. I didn't see one tank or sender set up for fuel injection to go behind the seat. I guess this is why the average guy puts a fuel cell under the bed in place of the spare. The market caters heavily to that.

**dave w** · 10-19-2022

1960 - 1966 Chevy Pickup - Fuel Sending Unit: https://www.tanksinc.com/index.cfm/p...rod/prd712.htm

**Overland** · 10-19-2022

Lots of those, nothing equipped with a pump or accommodation for extra wires and return. I'd modify the original before buying new, especially if I need to modify the new one anyway.

I didn't look long, but I'm honestly surprised it didn't show up on the usual sites alongside original equipment style.

Looks like I can get a replacement Suburban pump for ten dollars on rockauto to use for.mock up and testing, then tank flushing.

**dave w** · 10-19-2022

A return line similar to the picture below is both low cost and the optimal return line solution.
Picture is snippet from the .pdf previously posted. . . (possibly the picture is worth 1000 words?)

EFI Return.jpg

**tayto** · 10-20-2022

if you're tank doesnt have a sump/anti-slosh it's a waste of time IMO regardless if in tank or out of tank. most that run an external pump seem to run without an intake sump. having to keep the tank always above 1/2 way or you'll potentially have issues turning corners, hard acceleration or steep inclines is not for me but maybe you can live with it. i also do not like to listen to pump whine, but again maybe you can live with this too. definitely run a return line, your pump will be happier internal or external. do you have fab skills or know someone that does? i have bought a new tank added a sump and internal pump on efi conversions before.

**Overland** · 10-20-2022

Originally Posted by tayto

if you're tank doesnt have a sump/anti-slosh it's a waste of time IMO regardless if in tank or out of tank. most that run an external pump seem to run without an intake sump. having to keep the tank always above 1/2 way or you'll potentially have issues turning corners, hard acceleration or steep inclines is not for me but maybe you can live with it. i also do not like to listen to pump whine, but again maybe you can live with this too. definitely run a return line, your pump will be happier internal or external. do you have fab skills or know someone that does? i have bought a new tank added a sump and internal pump on efi conversions before.

I can see making a pump mount on the sender, but I'm working with maybe a three inch hole at the top of a flat tank turned sideways. I like to think I'm not as dumb as I look, but baffling in there has me baffled.

**357L98** · 10-25-2022

On pickup trucks with the tank in cab, I connect the return from the regulator to the filler vent with a T connector.

**AzDon** · 10-25-2022

I think the scheme you describe will fail to maintain the siphon effect on the tank supply line because you will be blowing pressurized fuel into your intake line and even if the loop was tight enough to maintain the siphon, you would be continually re-introducing pre-heated fuel instead of fresh cool fuel from the tank.....Have you considered drilling and tapping a hole in the top side of the filler neck (inside the cab) or sending unit plate and screwing in a return line fitting?

**357L98** · 10-25-2022

Originally Posted by AzDon

I think the scheme you describe will fail to maintain the siphon effect on the tank supply line because you will be blowing pressurized fuel into your intake line and even if the loop was tight enough to maintain the siphon, you would be continually re-introducing pre-heated fuel instead of fresh cool fuel from the tank.....Have you considered drilling and tapping a hole in the top side of the filler neck (inside the cab) or sending unit plate and screwing in a return line fitting?

Don, I checked out your page on the van project, very cool. I also tried connecting the return line back to the fuel pump inlet one time, and it did not work very well. As you thought, the fuel pump got hot and noisy after a short run time. I routed the return back to the filler vent and had no more problem.

**1project2many** · 10-25-2022

To clarify, I've never seen a gas engine plumbed this way, of which I've been into countless,

Rochester EFI. Low pressure pump supplies fuel to reservoir containing high pressure pump plus float and needle valve. Unused high pressure fuel is returned to reservoir.
http://www.oldcarmanualproject.com/m...0Injection.pdf
I believe the '59 - '64 Benz petrol mechanical injection systems were similar.

Here's a picture of the fuel system design in the early Bendix electrojection system. Pump in tank, regulator mid-system, return line directed to the tank.

I can see making a pump mount on the sender, but I'm working with maybe a three inch hole at the top of a flat tank turned sideways. I like to think I'm not as dumb as I look, but baffling in there has me baffled.

My solution was to leave the fuel level sender intact and to build a pump hanger beside it. After removing the fuel supply line from the original sender I brazed the hole shot. The '57 tank has a seam through the center, so I used a hole saw to cut two overlapping holes next to the fuel level sensor. The baffle I created is a simple open top box that's attached to the pump sender, sitting under the pump filter sock. I drilled holes in the lower corners of the box so fuel could flow in when the tank level is low. I still try to maintain fuel above 1/4 tank because this isn't perfect. But this reduced stalling while cornering when fuel was lower than 1/2 tank.

Fun reading:
https://67-72chevytrucks.com/vboard/...d.php?t=767225

http://67-72chevytrucks.com/vboard/s...efi+in+cab+tan