Fuel pressure question. Insufficient flow?

[IDIBRONCO]

I’m keeping the dual tanks but I’m setting it up so that the front tank is the main tank, while the rear tank (38 gallon) will simply pump into the front tank to replenish it. There will be a separate fuel pump manually controlled with a switch for this. I’m ditching the tank selector valve

I did all of this too. I used a Carter 4010 because they're relatively cheap. They aren't as good as they used to be, but they don't run very long at one time. I also don't worry much about the rear tank fuel level. If I have any doubts, or if it's been long enough that I can't remember, I just fill the rear tank. There is the possibility of overfilling the front tank this way, but I've only done that once. That was after a night of two hours of sleep, all day driving, temps in the lower 90s, and higher humidity than I'm used to most of the year. I was almost falling asleep and I just, plain forgot about it. I have no idea how long the fuel trail was behind me. Good thing that I was in rural Oklahoma when it happened! My lighted toggle switch didn't help that day. Normally, I see the light and won't forget. It's kind of tricky with my fuel gauge too. It will go WAY over full so if I shut it off at full, I won't get a full tank. I was going to suggest carrying a spare e pump, but you seem to have that covered. The picture below is of my fuel gauge when the front tank's about full. It's kind of blurry because I was driving when I took it. I had to because it's the only time that I see the gauge that high.

 

[DirtyWood]

I’m keeping the dual tanks but I’m setting it up so that the front tank is the main tank, while the rear tank (38 gallon) will simply pump into the front tank to replenish it. There will be a separate fuel pump manually controlled with a switch for this. I’m ditching the tank selector valve

How is this an improvement over a selector valve? I haven't had to investigate very far but is it impossible to find a good selector valve? Knock on wood several times but I've never had an issue with the FSV.

 

[TheRadBaron]

I haven’t had trouble with the selector valve on my truck but I’ve had trouble with them on trucks in the past. It’s a somewhat complex design and there’s a lot of potential for things to cause troubles. This is just my opinion on the matter, though.
I think my system design will be inherently more reliable and also has the benefit of having a redundant lift pump.
I really hate roadside breakdowns and I’m hoping to make this an extremely reliable truck because it’s going to see a lot of long trips. And a CCLB dually pulling a trailer really complicates things when you break down.

 

[franklin2]

Like everything else, quality is getting suspect and the switching valve's longevity is in question.

For the guy ditching the valve and using the dash switch, you can't do it unless you do a whole bunch of re-wiring. The switching valve had two jobs, switching the fluid lines between the tanks, and mechanically hooked to the valve motor was also a switch for the sending units. The electrical switching of the sending units was done by the valve on the frame down at the frame.

If you added a relay in place of the valve, and the relay was triggered by the dash switch, you might be able to wire it up to switch the sending units.

 

[Nero]

Well that is precisely what gasser variants do, instead of switching the valve, it changes which in-tank pump runs and reporting fuel level.

 

[franklin2]

Well that is precisely what gasser variants do, instead of switching the valve, it changes which in-tank pump runs and reporting fuel level.

Gasser switching valves are totally mechanical, no wires. The pressure from the in tank pumps mechanically moves the switching valve. The electrical switching of the sending units is done by the dash switch, not the valve on the frame like the diesels. That is why the diesel valve has so many wires, it has the sending unit wires down there along with the wires to move the valve motor.

So on a gasser the dash switch has lots of wires. On a diesel the frame mounted valve has lots of wires.

 

[TheRadBaron]

Like everything else, quality is getting suspect and the switching valve's longevity is in question.

For the guy ditching the valve and using the dash switch, you can't do it unless you do a whole bunch of re-wiring. The switching valve had two jobs, switching the fluid lines between the tanks, and mechanically hooked to the valve motor was also a switch for the sending units. The electrical switching of the sending units was done by the valve on the frame down at the frame.

If you added a relay in place of the valve, and the relay was triggered by the dash switch, you might be able to wire it up to switch the sending units.

Thanks for the insight on this. I hadn’t yet looked into what it would take but I’m good with wiring and one way or another it should be electrically simple to be able to toggle between two sending units. Whether than means adding a relay of some sort like you mention, or installing a different switch in the dash to get things to work correctly, it shouldn’t be a big deal.

 

[franklin2]

Relay would work, but keeping it out of the weather may take a sealed box or something. Or moving and extending the sending unit wiring up into the cab to keep the relay out of the weather, or adding a switch on the dash, both requiring extending the wiring.

Just expect your ears to burn when the next owner see's all this custom wiring. I am sure you have seen posts on here, where does this wire go? Or what is this wiring for?

 

[TheRadBaron]

Relay would work, but keeping it out of the weather may take a sealed box or something. Or moving and extending the sending unit wiring up into the cab to keep the relay out of the weather, or adding a switch on the dash, both requiring extending the wiring.

Just expect your ears to burn when the next owner see's all this custom wiring. I am sure you have seen posts on here, where does this wire go? Or what is this wiring for?

I’ve never really considered that when I modify my vehicles. Plus, this truck isn’t going anywhere. It’s my late father’s truck and it’s been in the family for a long time. Lots of good memories.
I keep really detailed records of all the maintenance and modifications I do to my vehicles. This includes wiring details when I change things around. This is mostly for my reference so when it’s 10 years down the road and I’ve forgotten the details of what I’ve done I have good reference material.

I’m sure I can get it wired up in a way that’ll be weathertight and durable. I’m a lifelong mechanic, and former military aircraft mechanic, and I’m meticulous about the work I do to my stuff. Aviation or marine grade crimp connections done with the proper tools, adhesive heat shrink, modern automotive connections with sealed wire entries and sealed connector housings, etc.

 

[lotzagoodstuff]

I'll throw in .02 here: the selector valves seem to always fail due to the actual fuel valve malfunctioning. You can call it age, you can say they are typically contaminated with bits from the showerheads and/or anything that made it's way into your fuel tanks (perhaps algae helping you out), so if I was going to try to rework a twin fuel tank scenario, I think I'd make the dash switch just switch the electric sending unit to display fuel level, and leave the actual switching to a mechanical 6 port selector valve made of brass that will likely outlive Methuselah. For instance: https://www.mrostop.com/uploads/parker_pdfs/k24.pdf

In summary: separate the two functions of the factory selector valve, prioritizing the mechanical ball/diversion valve as that's the part that will strand you. Even if you got showerhead pieces (or maybe an appropriately sized cockroach) lodged in your brass selector valve, you would most likely "guillotine" the pieces when you turned the lever, or you would notice and have a relatively easy place to remove/clean/reinstall. If your sending unit switch fails, it ain't the end of the world as you can just count mileage with your odometer and stop for fuel as needed. If you don't want to get out of your cab to actuate the ball valve, they make handle extensions and you could mount it so that you could actuate this from inside your cab while driving if that's your particular priority (zombie apocalypse?).

If you could incorporate a single fuel pump that would draw through the brass selector valve, I think you'd have conquered simplicity and durability, but that's my opinion, and you know what they say about those.

Best of luck whichever way you decide to go.