How are the factory dual saddle fuel tanks supposed to be routed?

[WranglerTJForum]

When I said early and late I should have said return or no return. Wasn't thinking. But now that I am he needs to verify whether his injection requires a fuel return,it probably does. If so he's going to have to go with the later style valve.

I’ve got the Sniper EFI which does require a return, but those Holley fuel pumps have a return built into them. I suppose they ought to for what they cost.

 

[Ricko1966]

I’ve got the Sniper EFI which does require a return, but those Holley fuel pumps have a return built into them. I suppose they ought to for what they cost.

You could use 87 senders and walbro intank pumps,but you'd need a 6 port switch

 

[Grit dog]

Didn’t see til now you likely or certainly have one aftermarket tank based on the switch pic you posted. Does one of them things not look like the other? You never acknowledged what @AuroraGirl gave you for info. You state you have dual 16s but unless 73 being first year didn’t have dual tanks, 74 and up had the GM rocker switch or it was add on aftermarket.
Also probably means that the pumps you ordered (when you assume in tank hp pumps but your other pics suggest the inline pump is hi pressure as the cob goblin who plumbed this thought to use high pressure hose clamps on it vs worm drives by the cobbled up transfer switch) won’t fit the aftermarket tank pretty sure?
This is not one of those “order all the pasts first so you can be efficient”. This is a figure out what you got and what you want to do about it. Get it all accessible and planned and then maybe you have a shot at getting it right the first time. And Idfk what the transfer solenoid is doing. Only half hooked up.
Seriously. Unless you like working upside down for days with chit falling in your eyes and crawling out from under the truck 1,234 times, pop the bed off and then work EVERYTHING from the efi system back to the tanks.
Also you can easily do twin tanks with one frame rail mounted pump. Cheaper and simpler than dual hp pumps especially when one won’t fit unless you get an oe tank or a universal in tank hp pump to work.

Also that other dude was right. At this point a single fuel cell may be easier. But Wyoming is a big state and that’s an 8mpg truck even with EFI, downhill with a tail wind. I wouldn’t take er too far out of town without some jerry cans if you go to a baby size fuel cell. Lol

If you’re “very good at wiring” then plumbing a fuel system is like circuits 101 for dummies. A literal walk in the park of you’re saavy with circuits.
Start by finding out what you have. And like I tell my kids, write **** down, label ****, and the computer can’t replace your brain! Lol.

 

[Grit dog]

You could use 87 senders and walbro intank pumps,but you'd need a 6 port switch

Except neither he nor we even know if both tanks are GM oe style tanks.
Also @WranglerTJForum, don’t waste your $ on poly tanks. If they even make 16 gal ones. The 20 gal ones are 3.5x the cost of steel tanks. Just a complete waste of money. If OE tank lasts 25-50+ years and you’re not taking a salt bath all winter in your fancy high $ classic truck there is no point. Plus even if you did, the truck would rust out before a new $100 tank would.

 

[WranglerTJForum]

Except neither he nor we even know if both tanks are GM oe style tanks.
Also @WranglerTJForum, don’t waste your $ on poly tanks. If they even make 16 gal ones. The 20 gal ones are 3.5x the cost of steel tanks. Just a complete waste of money. If OE tank lasts 25-50+ years and you’re not taking a salt bath all winter in your fancy high $ classic truck there is no point. Plus even if you did, the truck would rust out before a new $100 tank would.

Point taken! I’ll just buy some steel tanks with baffles.

I’m looking at the tanks now. One of them is the factory tank and the other one is a brand new factory reproduction tank.

 

[WranglerTJForum]

Didn’t see til now you likely or certainly have one aftermarket tank based on the switch pic you posted. Does one of them things not look like the other? You never acknowledged what @AuroraGirl gave you for info. You state you have dual 16s but unless 73 being first year didn’t have dual tanks, 74 and up had the GM rocker switch or it was add on aftermarket.
Also probably means that the pumps you ordered (when you assume in tank hp pumps but your other pics suggest the inline pump is hi pressure as the cob goblin who plumbed this thought to use high pressure hose clamps on it vs worm drives by the cobbled up transfer switch) won’t fit the aftermarket tank pretty sure?
This is not one of those “order all the pasts first so you can be efficient”. This is a figure out what you got and what you want to do about it. Get it all accessible and planned and then maybe you have a shot at getting it right the first time. And Idfk what the transfer solenoid is doing. Only half hooked up.
Seriously. Unless you like working upside down for days with chit falling in your eyes and crawling out from under the truck 1,234 times, pop the bed off and then work EVERYTHING from the efi system back to the tanks.
Also you can easily do twin tanks with one frame rail mounted pump. Cheaper and simpler than dual hp pumps especially when one won’t fit unless you get an oe tank or a universal in tank hp pump to work.

Also that other dude was right. At this point a single fuel cell may be easier. But Wyoming is a big state and that’s an 8mpg truck even with EFI, downhill with a tail wind. I wouldn’t take er too far out of town without some jerry cans if you go to a baby size fuel cell. Lol

If you’re “very good at wiring” then plumbing a fuel system is like circuits 101 for dummies. A literal walk in the park of you’re saavy with circuits.
Start by finding out what you have. And like I tell my kids, write **** down, label ****, and the computer can’t replace your brain! Lol.

Yes, you’re right. At this point I am just going to take everything out and see what I’ve got. Winter is coming and here in Wyoming that means I won’t be driving this truck for a number of months.

I can say for certain I’m going to replace the tanks with these ones:

1973-81 Chevy and GMC Pickup Truck Fuel Injection Gas Tank - 6' Short Box

Tanks, Inc. manufactures fuel system components and polyethylene, steel and stainless steel gas tanks for street rods and special interest vehicles.

www.tanksinc.com

Those are OE style but they are baffled which is something I want.

I ordered the correct pollack valve, so now the question is fuel pumps.

Is there any advantage to having two of those Holley in-tank fuel pumps as oppose to a single external fuel pump? Cost is obviously a big advantage with the single external fuel pump, but I’m going to say that at this point money isn’t an issue. I would rather just do it once and do it right.

One thing I can say for sure is that this old K10 has made me thoroughly enjoy working on vehicles again. I grew up working on old cars but as I got older I started buying newer cars which greatly turned me off from doing my own wrenching. They’re almost impossible to work on anymore the way they pack everything in there.

It’s such a breath of fresh air to get under my truck and be able to easily access everything. I never thought I would enjoy working on vehicles again but this truck has changed that. What a breath of fresh air.

 

[Grit dog]

Yes older vehicles are generally easier to work on. For the most part.
Those tanks look like they’d work of course.
Good news if it has both OE style tanks then you have the brackets already.
There are many ways to go about it though and if replacing tanks is not necessary (they don’t wear out unless they rust out). Baffles are needed unless you spring for the in tank pumps with a reservoir like you suggested before. $ on pumps vs $ on new tanks but you have redundant pumps.
The tanks you posted are pretty spendy. I think you can get OE style 16g with baffles for half $ or less.
One pump is ok too. Baffled tanks, carb fuel pickup/senders and a good pump which you might have already based on your pic. If mounted close to the tanks and as low as possible it will work reliably.
All cost vs benefit vs preference vs difficulty.
You said $ is no object but….I don’t think that way regardless of cost unless it’s an immediate necessity.

 

[Ricko1966]

87 tanks are factory baffled and cheap. In tank pumps typically live longer. Pumps push better than they pull. In tank they have one job push fuel. External they have to pull fuel and push fuel. 99 percent of everything uses in tank pumps and has for decades even the stuff that does have an external pump factory, has a pusher pump in the tank. I can't believe that all the manufacturers would do this just for fun.

 

[Broken85]

When I said early and late I should have said return or no return. Wasn't thinking. But now that I am he needs to verify whether his injection requires a fuel return,it probably does. If so he's going to have to go with the later style valve.

12-308 are in tank pumps so no return line. He should be good.

Yes, you’re right. At this point I am just going to take everything out and see what I’ve got. Winter is coming and here in Wyoming that means I won’t be driving this truck for a number of months.

I can say for certain I’m going to replace the tanks with these ones:

1973-81 Chevy and GMC Pickup Truck Fuel Injection Gas Tank - 6' Short Box

Tanks, Inc. manufactures fuel system components and polyethylene, steel and stainless steel gas tanks for street rods and special interest vehicles.

www.tanksinc.com

Those are OE style but they are baffled which is something I want.

I ordered the correct pollack valve, so now the question is fuel pumps.

Is there any advantage to having two of those Holley in-tank fuel pumps as oppose to a single external fuel pump? Cost is obviously a big advantage with the single external fuel pump, but I’m going to say that at this point money isn’t an issue. I would rather just do it once and do it right.

One thing I can say for sure is that this old K10 has made me thoroughly enjoy working on vehicles again. I grew up working on old cars but as I got older I started buying newer cars which greatly turned me off from doing my own wrenching. They’re almost impossible to work on anymore the way they pack everything in there.

It’s such a breath of fresh air to get under my truck and be able to easily access everything. I never thought I would enjoy working on vehicles again but this truck has changed that. What a breath of fresh air.

I tried the inline pump before I went to the in tank. You have to put it after the pollack valve on the frame. The good news is that there is plenty of room. The bad news is I couldn’t get it to work very well.

The inline pumps push fuel, they don’t pull it so you are beholden to how Fast Fuel can siphon out of the tank, through the valve and feed into the pump. If you put a hole in the bottom of the tank and feed an inline from there, those inline pumps would work perfect but who the hell would ever do that. And they are noisy, and they fail because they get hot. And then you also need to add a pressure regulator for the Sniper and run a return line back to the tank.

Buy once, cry once. Wire it and plumb it the way I showed you. You will have redundancy. If one pump, or one relay goes the second side is independent and will get you home. In tank pumps stay cool and they are internally regulated, no pressure regulator needed.

Good job on finding that tank!

 

[Ricko1966]

12-308 are in tank pumps so no return line. He should be good.

I tried the inline pump before I went to the in tank. You have to put it after the pollack valve on the frame. The good news is that there is plenty of room. The bad news is I couldn’t get it to work very well.

The inline pumps push fuel, they don’t pull it so you are beholden to how Fast Fuel can siphon out of the tank, through the valve and feed into the pump. If you put a hole in the bottom of the tank and feed an inline from there, those inline pumps would work perfect but who the hell would ever do that. And they are noisy, and they fail because they get hot. And then you also need to add a pressure regulator for the Sniper and run a return line back to the tank.

Buy once, cry once. Wire it and plumb it the way I showed you. You will have redundancy. If one pump, or one relay goes the second side is independent and will get you home. In tank pumps stay cool and they are internally regulated, no pressure regulator needed.

Good job on finding that tank!

Wow I just looked at the price of those holley pumps. I'd buy an external FPR a 6 port Pollak valve and 2 ep 381 pumps on 87 senders,I can buy all that for the price of 1 Holley pump and probably have change .

 

[Grit dog]

87 tanks are factory baffled and cheap. In tank pumps typically live longer. Pumps push better than they pull. In tank they have one job push fuel. External they have to pull fuel and push fuel. 99 percent of everything uses in tank pumps and has for decades even the stuff that does have an external pump factory, has a pusher pump in the tank. I can't believe that all the manufacturers would do this just for fun.

100% agree with you. However that does not mean that an external pump mounted as close to the pollack valve downstream and as low as reasonably possible (doesn’t have to hang below the frame although lower than the fuel level would be ideal) won’t work well and reliably.
In tank pumps are ideal but been poor boying effective solutions for quite some time. Plus they do make a couple pumps designed to pull fuel.
As some anecdotal recent evidence, the 86 (carbed engine, no fuel pump provision) has to run an electric pump. Electric pump was installed under the hood and wired up all janky when we bought it.
Pumps didn't last. I re plumbed it just downstream of the tank valve and gave it clean power.
“For the time being” I just reused the relatively new little Edelbrock $50 inline pump since we were tearing it down for paint. That was 5 years ago. Only maybe 5000 miles since then but working like a charm still, prior to that they were lasting about 500 miles.
Again not the “best” way but it would be pretty bulletproof with a quality pump.
And even if the lifespan was not indefinite, makes it cheap and easy to replace.
As further evidence, back in the day, my Blazer plow truck winter beater had a worn cam lobe for the fuel pump. Wouldn’t pump gas with the mechanical pump. I installed a Carter electric pump back by the fuel tank and gave it good clean power. Put at least 30k miles on that thing in about a year. Didn’t know better that it “shouldn’t have worked.” Including weekly road trips, daily commutes and the equivalent of a few weeks of running continuously without being shut off (snow plowing for 12-24hr straight).
One of the few things that did still work on that truck when I got rid of it was the fuel pump. Unlike my last boat with an EP381 style pump that made it about 350 engine hours compared to the previous boat pullling fuel about 6’ and not below tank pickup level with an external pump (as designed) that was still pumping when we sold it with about 750 engine hours.

 

[LJ69]

Yep, that’s me. I decided I’m just going to keep the dual saddle tanks, I just have to figure out how to get the system working.

That setup you linked to mentions it’s for 74 and up. The one that is on my truck now (though it isn’t hooked up) looks exactly like this:

1973-80 Square Body Chevy & GMC Truck Dual Tank Selector Valve, Single Wire, 3 Port without Fuel Return Lines

1973-80 Square Body Chevy & GMC Truck Dual Tank Selector Valve

www.usa1industries.com

I’m assuming this is the right part?

I may go with those baffled tanks at some point but right now I just have to get it to work.

Since the previous owner installed a Holley Sniper EFI he would have had to have changed out the fuel pump in the main tank at the very least. I’m guessing that since the main tank is new and shiny looking that he used an in-tank fuel pump when he purchased that new main tank and likely just left the aux tank alone and unfunctional which is why nothing works.

Sounds like I’m going to have to drop both tanks and see what I’ve got going on here.

You probably should think about switching to the '87 style switching valve. It has all the fuel ports for feed and return and electric connectors for pump and sending unit for each tank. Each tank individualy converges at the switching valve. The main/auxiliary switch in the cab is wired to the switching valve and, depending on witch side is pushed, energizes one tank and disables the other. So you are correct on needing a fuel pump for each tank. The Holly snipers are fussy on their fuel pressure. It needs to be 60 psi. The Holley system should have a fuel pressure regulator installed on the feed line somewhere. When you do your dual tank install, make sure the pressure regulator is installed between the selector valve and the fuel injectors so it can regulate after fuel flows through the selector valve. It might be helpful to put an inline fuel pressure guage close to the intake at least for instalation purposes to make sure you are getting proper pressure from each tank.

 

[WranglerTJForum]

You probably should think about switching to the '87 style switching valve. It has all the fuel ports for feed and return and electric connectors for pump and sending unit for each tank. Each tank individualy converges at the switching valve. The main/auxiliary switch in the cab is wired to the switching valve and, depending on witch side is pushed, energizes one tank and disables the other. So you are correct on needing a fuel pump for each tank. The Holly snipers are fussy on their fuel pressure. It needs to be 60 psi. The Holley system should have a fuel pressure regulator installed on the feed line somewhere. When you do your dual tank install, make sure the pressure regulator is installed between the selector valve and the fuel injectors so it can regulate after fuel flows through the selector valve. It might be helpful to put an inline fuel pressure guage close to the intake at least for instalation purposes to make sure you are getting proper pressure from each tank.

Yep, I ordered the 87 style valve after doing research on this.

The Holley fuel pumps I ordered have internal fuel pressure regulators that are set to 58 psi per Holley:

https://www.holley.com/products/fuel_systems/fuel_injection/sniper_efi/ignition_and_fuel_systems/fuel_systems_and_accessories/muscle_car_efi_modules/parts/12-308

 

[75BEASTK20]

I have a 75 Custom Deluxe K20 with factory dual tanks. I had wiring "issues" as well. IMO, the best way to fix all that was to replace the FACTORY pickups in the NEW tanks, buy the correct transfer pump that mounts in the frame rail......and from there it goes to the mechanical fuel pump. I also replaced the original in cab fuel switch (FACTORY) and kept the old one as a spare just in case. The only thing I changed was the fuel pump to a Holley blue with a pressure regulator and DON'T FORGET FUEL FILTERS ! This is probably the easiest way to get back to 'normal'. You can use the mechanical fuel pump if you want to..........but lately the quality of aftermarket mechanical fuel pumps has been very sketchy. I went through THREE pumps before I said to hell with it and went to an electric fuel pump and a pressure regulator. I installed a much higher horsepower engine and didn't want any fuel starvation. These old square bodies like to drink. So , in short I would say.......TRY to remain as much factory as you can. They worked well when new and occasionally you might have to replace a rotten fuel line. But I'm running stainless 3/8" fuel line and don't have much exposed rubber anywhere. Tuck everything up nicely. Wire it NEATLY. Protect the wires! It can be frustrating at times. Finding a GOOD ground is essential. 90% of these fuel problems are ground related. Take your time and use all the drawings the other fellas have posted and you'll be ok. Good luck.

 

[Casca2525]

https://classicparts.com/1974-95-gas-tank-selector-valve-kit?srsltid=AfmBOoovWOThptGajwvUEXtf_sfPhZVEA2S2MO_xKG0LV84Joargt_Br

thanks for this, I am in a similar boat, quick question did any of these trucks come with 3 tanks? my Scottsdale w 454 has 2 filler doors on drivers side 1 in front of the flare saddle and currently only tank and one at the back of the flare, like a logical spot for a rear tank, as well as a 3rd on the right where the right side saddle tank would be?

I ask because I travel regularly from eastern Ontario to south western Ontario, pulling a 26ft house trailer, about a 1600km round trip, so I'm thinking 3 tanks could be handy