Care to speculate on tbi fuel system plumbing?

**Six_Shooter** · 10-18-2022

I see fuel pressure regulation issues if you are T-ing the return line back into the fuel pump feed. This IS a restriction and restrictions, even ones that could potentially flow both into and out of the tank will cause issues. Even if your pressure seems to be what it's supposed to be, I could potentially see a problem with reliable fuel supply due to the feed from the tank needing to flow both into and out of the tank continuously.

It's not difficult to add a return line to a sender unit. A drill, some hard line and someway to seal it up, which can be something like JBweld, or epoxy will create a trouble free system that you won't have to second guess.

**Fast355** · 10-18-2022

I had one of those Ford frame mounted pumps when I first converted my 83 G20 to TBI. It was garbage and loud. It lived a short life without the boost pump supplying fuel to its inlet. I switched it out for a TBI van tank and fuel lines. Used a Vortec fuel pump on the TBI sending unit.

**Overland** · 10-19-2022

I think it comes down to the suction side. Every high pressure pump I've ever seen had the return ported back into the pump inlet. The difference is pressurized or gravity supply. There's always fluid at the inlet. If the tank had a bung in the bottom, I think it would be okay.

Cavitation will kill it in short order for sure. Also, I think I'd rather pay more for a low pressure pump than try to make do with the excess volume, and probable noise, of a higher output model.

My primary goals here are reliability and economy. It's getting single exhaust. Totally stock Suburban engine, zero illusions of high performance.

Also not changing the location of the tank. I know it's popular, but I wouldn't have a filler in the bed even if there was room underneath for a fuel tank.

**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

**Six_Shooter** · 10-20-2022

Originally Posted by Overland

I think it comes down to the suction side. Every high pressure pump I've ever seen had the return ported back into the pump inlet. The difference is pressurized or gravity supply. There's always fluid at the inlet. If the tank had a bung in the bottom, I think it would be okay.

Cavitation will kill it in short order for sure. Also, I think I'd rather pay more for a low pressure pump than try to make do with the excess volume, and probable noise, of a higher output model.

My primary goals here are reliability and economy. It's getting single exhaust. Totally stock Suburban engine, zero illusions of high performance.

Also not changing the location of the tank. I know it's popular, but I wouldn't have a filler in the bed even if there was room underneath for a fuel tank.

I've never seen a return line plumbed back into a fuel pump inlet. Every vehicle I've worked on, or looked at, and it's many, many vehicles, has the return line back into the tank itself, so there is little to no restriction on the return line, allowing the bypass regulator to perform it's job easily.

**NomakeWan** · 10-20-2022

Perhaps he meant near the pump inlet? I know on my Corvette, the return line is plumbed to a metal line that exits right next to the filter sock on the pump inlet. Yes, it's technically exiting into the tank, but it's also exiting right next to the pump inlet.

**1project2many** · 10-20-2022

I have worked on diesels with the return line connected to the pump inlet. This method was common in the 50's and '60s for sure, but not so common today. I believe my '80s Mercedes diesel OM617 plumbed the return line to the high pressure pump inlet as well.

Mercruiser EFI engines in the late '90s used a "fuel module" which contained a reservoir, a needle valve connected to a float, and a high pressure pump. The reservoir was filled by a traditional mechanical pump on the block. I used one of these systems when I installed a mercruiser manifold and ecm in my '67 Chevelle. It worked well for me. Mercruiser decided the system needed improvement though and developed "fuel coolers" to be used in later systems. Internet folks predicted that I might have trouble if I ever cruised through the southwestern states. I never had the opportunity to try.

I have been posting for years about my experience adding a return line and electric pump to a tank never designed for such things. I was young when I did this, and the internet was literally a phone call to another town away so there was little to guide me. Long story short, without baffles and vapor handling the system was not as successful as I'd hoped. Without a reservoir to hold fuel, the engine stumbled whenever fuel level fell below pump pickup level. Without vapor handling, the tank built pressure and fuel vapor escaped as fuel warmed up. I added a fuel cooler on the return line and a baffle in the tank for some improvement but today I would do it differently. I would build / buy / scrounge a remote fuel reservoir similar in principal to the Mercruiser unit. For reference, this is in a '57 Chevy truck, also with an in-cab tank, which I still own.

Edelbrock makes a system similar to the Mercruiser module. https://www.edelbrock.com/adjustable...psi-36032.html It's spendy. There are companies that make small, frame mounted remote tanks which contain the high pressure pump and act as a reservoir. I'm not having good luck searching now but they are out there. Recently I have found that you can buy a weld-in retaining ring to use the Dodge / GM remote "fuel bucket" system. The fuel bucket system really solved a bunch of issues for GM by providing a single point for pump, sender, return, and baffling within the tank. There is a stainless version found here: https://rickstanks.com/product/weld-in/?v=47e5dceea252 Searching can locate other versions, possibly less expensive. Will it fit in the '62 tank?? Possibly?

I would not place a filter on the inlet side of the pump. I have had issues with this in the past. Most electric fuel pumps are not good at creating suction. Spinny pumps generally work because the pressure of the fuel around the pump forces fuel into the pump body even as the vanes are forcing fuel out to the engine. An electric diaphragm pump would likely have better luck pulling fuel through a filter and could be connected to a remote reservoir with a float and high pressure pump.

In talking this through, your original idea might be very doable if you use a diaphragm pump to supply low pressure fuel to the Ford inline pump previously mentioned and use a 99+ Corvette fuel filter with return and pressure regulator built in connected between the low and high pressure pumps. The only concern I would have would be how the system would perform at low fuel levels. Without a way to eliminate fuel slosh, or to supply a temporary supply of fuel while the pickup tube is exposed in the tank, you're risking engine stumble.

**Overland** · 10-20-2022

Y'all are golden. I'm fabricating everything which is not original or factory equipment. I'm not bad at making my own parts and tools as need be and have access to a machine shop.

Yes, my return line idea went not to the pump inlet but to the filter housing on said inlet. I have my own reservations regarding using a spinny pump to pull fuel through a filter but this was, I supposed, a reservoir so to speak. I'm thinking spin on filter base with two inlets.and two outlets, one outlet plugged, within six or eight inches of the pump.

This becomes too convoluted for me when adding another pump style to support the other. Yes, I can do it, but that doesn't mean I should.

To clarify, I've never seen a gas engine plumbed this way, of which I've been into countless, but most every diesel ever made nearly up to the common rail era where I look away. Pressure washers are plumbed this way though with an unloading control in place of a regulator. They circulate directly back into the inlet until loaded. They also have pressurized or gravity feed.

Rather than drilling the sending unit, why not drill the tank instead for gravity feed.to the pump? Then I could use the pickup tube for a return line.