Advice Needed: Adding stock 19 gal rear fuel tank to single tank truck

[Tyler]

Please poke holes in my plan, Bullnosers!

Some other guys have done projects similar to this but without closure on the thread, so I don't have the full story. And I'm looking to do it just a little different.

I found a new EFI model rear fuel tank in a donor truck at a local JY. My truck only has the single 16 gal tank and was carbureted (see signature).

I plan to remove the crossmember, tank, straps, spare tire mount, etc. from the donor truck as well as the wiring harness and heater/blower/fuel tank selector module from the dash. Then install into my truck. I THINK I can use a relay setup to power the fuel pump in this rear tank, routed through a toggle switch that I will put on the dash somewhere. Then, I will route the 19 gal tank fuel pump outlet directly into the 16 gal side tank sending unit (this is no longer used due to converting to Holley Sniper and retro-fit in tank fuel pump and the screen has been removed). This allows me to fill the side tank from the rear tank using the switch on the dash and the stock in-tank fuel pump from the 19 gal rear EFI tank.

I intend on cutting a hole in the bed behind the wheel well and mounting a filler neck from underneath (by my eyeballing, it should line up pretty close to the rear tank fill location on dual tank trucks).

I THINK I can wire the existing 16 gal side tank sending unit level detection to the scavenged JY dash unit and then run a parallel set of wiring to the "new" rear tank sending unit. This will allow me to see the level in the rear tank when needed so that I don't run the fuel pump dry.

Of course, I'll post up pics and lessons learned when I'm done.

I know I haven't considered or checked if the dash module from the donor truck will connect to my non-AC unit and probably a few other finer points as well. Inertia switch? Overflow?

Prove me wrong. Prove me right. Advice? Things I haven't considered? Standing by...

[ArdWrknTrk]

I think you need to hear from Dave (Fuzzface2)

AFAIK he's the one here who has put dual tanks in a SWB truck... but he doesn't have an aftermarket Sniper setup.

 

[Rusty_S85]

I thought of trying to do a dual tank setup but I found them to be a pain on the sniper install I did on a 78 GMC with dual tanks, switching valve is rated for 50 PSI from a 80s pickup but the valve wouldnt switch with the engine running due to the 50 psi fuel pressure. I theorize it would probably work better as a puller pump through the switching valve but that also means a noisier pump, a pump that wont last as long as it is more prone to running hot.

One Idea I had on my short wheelbase truck as I thought of getting the large 50 gallon I think it is rear tank from a place like LMC and then use a transfer pump to pump fuel from that tank into my saddle tank and just use my saddle tank as the supply tank for my Sniper. Down side to this is you would need quite a large volume pump to be able to fill the saddle tank up in quick order and then you would need some kind of safety to shut the transfer pump off in case you dont catch it and switch it off manually.

Personally Ive been looking at having the 16 gallon saddle tank lengthened on the front end. Measurements I took shows I should be able to add 3 inches to the front of the saddle tank which if my calculations are correct should turn the 16 gallon saddle tank into a 21 gallon saddle tank. Only draw back in my mind on this is all that extra weight if the straps could handle that and if that extra 5 gallons would cause the truck to sit with a lean to the driver side. In any case I know the saddle tank on mine will have to be cut open regardless to weld in a baffle as 85-86 trucks didnt have baffled fuel tanks, they used a lift pump to a pump reservoir that the high pressure fuel injection pump on the frame sucked from and I wont be doing this on my truck.

But in the end that is one of the reasons I decided to scrap my idea of adding a second aft tank to my truck. Ever since I did that 78 GMC with that 85/86 GM switching valve and found it would not switch on the fly I just have no idea how I personally could add a dual tank to my truck and have a functional switching valve without putting the pressure pump on the frame rail.

If you do it the way I was thinking of on mine and use a transfer pump to fill your saddle tank from the aft tank what you can do is get a AN bulkhead fitting and drill a hole in the top of your saddle tank and use one of those bulkhead fittings from the inside to the outside to allow an attachment point for the transfer line from the rear tank. Great thing about doing the AN bulkhead connector which some come with sealing washers for this kind of thing you can use another AN hose end on the inside with a hose long enough to keep it near the bottom of the tank to prevent aeriation.

[FuzzFace2]

I thought of trying to do a dual tank setup but I found them to be a pain on the sniper install I did on a 78 GMC with dual tanks, switching valve is rated for 50 PSI from a 80s pickup but the valve wouldnt switch with the engine running due to the 50 psi fuel pressure. I theorize it would probably work better as a puller pump through the switching valve but that also means a noisier pump, a pump that wont last as long as it is more prone to running hot.

One Idea I had on my short wheelbase truck as I thought of getting the large 50 gallon I think it is rear tank from a place like LMC and then use a transfer pump to pump fuel from that tank into my saddle tank and just use my saddle tank as the supply tank for my Sniper. Down side to this is you would need quite a large volume pump to be able to fill the saddle tank up in quick order and then you would need some kind of safety to shut the transfer pump off in case you dont catch it and switch it off manually.

Personally Ive been looking at having the 16 gallon saddle tank lengthened on the front end. Measurements I took shows I should be able to add 3 inches to the front of the saddle tank which if my calculations are correct should turn the 16 gallon saddle tank into a 21 gallon saddle tank. Only draw back in my mind on this is all that extra weight if the straps could handle that and if that extra 5 gallons would cause the truck to sit with a lean to the driver side. In any case I know the saddle tank on mine will have to be cut open regardless to weld in a baffle as 85-86 trucks didnt have baffled fuel tanks, they used a lift pump to a pump reservoir that the high pressure fuel injection pump on the frame sucked from and I wont be doing this on my truck.

But in the end that is one of the reasons I decided to scrap my idea of adding a second aft tank to my truck. Ever since I did that 78 GMC with that 85/86 GM switching valve and found it would not switch on the fly I just have no idea how I personally could add a dual tank to my truck and have a functional switching valve without putting the pressure pump on the frame rail.

If you do it the way I was thinking of on mine and use a transfer pump to fill your saddle tank from the aft tank what you can do is get a AN bulkhead fitting and drill a hole in the top of your saddle tank and use one of those bulkhead fittings from the inside to the outside to allow an attachment point for the transfer line from the rear tank. Great thing about doing the AN bulkhead connector which some come with sealing washers for this kind of thing you can use another AN hose end on the inside with a hose long enough to keep it near the bottom of the tank to prevent aeriation.

When I get on my pc I will reread this and post what I think.

Dave ----

[Tyler]

I thought of trying to do a dual tank setup but I found them to be a pain on the sniper install I did on a 78 GMC with dual tanks, switching valve is rated for 50 PSI from a 80s pickup but the valve wouldnt switch with the engine running due to the 50 psi fuel pressure. I theorize it would probably work better as a puller pump through the switching valve but that also means a noisier pump, a pump that wont last as long as it is more prone to running hot.One Idea I had on my short wheelbase truck as I thought of getting the large 50 gallon I think it is rear tank from a place like LMC and then use a transfer pump to pump fuel from that tank into my saddle tank and just use my saddle tank as the supply tank for my Sniper. Down side to this is you would need quite a large volume pump to be able to fill the saddle tank up in quick order and then you would need some kind of safety to shut the transfer pump off in case you dont catch it and switch it off manually.Personally Ive been looking at having the 16 gallon saddle tank lengthened on the front end. Measurements I took shows I should be able to add 3 inches to the front of the saddle tank which if my calculations are correct should turn the 16 gallon saddle tank into a 21 gallon saddle tank. Only draw back in my mind on this is all that extra weight if the straps could handle that and if that extra 5 gallons would cause the truck to sit with a lean to the driver side. In any case I know the saddle tank on mine will have to be cut open regardless to weld in a baffle as 85-86 trucks didnt have baffled fuel tanks, they used a lift pump to a pump reservoir that the high pressure fuel injection pump on the frame sucked from and I wont be doing this on my truck.But in the end that is one of the reasons I decided to scrap my idea of adding a second aft tank to my truck. Ever since I did that 78 GMC with that 85/86 GM switching valve and found it would not switch on the fly I just have no idea how I personally could add a dual tank to my truck and have a functional switching valve without putting the pressure pump on the frame rail.If you do it the way I was thinking of on mine and use a transfer pump to fill your saddle tank from the aft tank what you can do is get a AN bulkhead fitting and drill a hole in the top of your saddle tank and use one of those bulkhead fittings from the inside to the outside to allow an attachment point for the transfer line from the rear tank. Great thing about doing the AN bulkhead connector which some come with sealing washers for this kind of thing you can use another AN hose end on the inside with a hose long enough to keep it near the bottom of the tank to prevent aeriation.

Rusty, my plan was to use the in tank pump for the rear tank as a transfer pump.  I would manually control it from a toggle switch that I'll put on the dash (probably on the center portion above the radio).The in-tank pump would push fuel directly into the saddle tank through the saddle tank sending unit tube, which is now retired and capped off.

 

 

The stock dash switch on the heater/blower control unit would only be used for fuel level indication so I could see level in both tanks when needed.

 

 

 

 

 

 

[myrl883]

This seems like a good plan. Much simpler than making all of the otherwise necessary plumbing connections for a normal dual tank setup.

You'll just have to be careful of the overflow potential since the rear tank is larger than the front. This is (also) a good thing because you shouldn't ever run the rear tank dry and kill a fuel pump.

[FuzzFace2]

This seems like a good plan. Much simpler than making all of the otherwise necessary plumbing connections for a normal dual tank setup.

You'll just have to be careful of the overflow potential since the rear tank is larger than the front. This is (also) a good thing because you shouldn't ever run the rear tank dry and kill a fuel pump.

Ok on PC now

What do they do on the FI trucks with dual tanks from the factory?

I think the tank valve is switched by the fuel PSI IIRC and this also changes the gauge.

I just don't know what that PSI is but why not do that set up on the truck?

So you want to get everything for the rear tank like I think you said you got.

Tank, straps, the cross member just in front of the tank the straps go to.

As for the wiring. On my truck (81 F100) the dual tank wiring is all part of the main & frame harness.

My parts truck was also a 81 F100 so it was just swap harnesses and I was good to go.

Now I think you are using a newer dual tank harness in your truck so I don't know what you will run in to or have to make work.

I think to go through all the work to have a level reading on the rear tank and have that pump transfer gas to the from is a lot of work.

If me and I could not get both tanks to work like the factory did I would set up the rear 19 gal. as the main and the 16 gal. as the back up and transfer it to the rear.

On the fill tube you are going to fill through the wheel opening?

How much road dirt is going to be kicked up on it?

Did you get all that from the parts truck?

I like the clean factory look and why I molded the rear filler door into the fender.

If you have a 2nd door assy. you could have a shop or you mount it in your bed side.

I know not a lot of help here sorry.

If there is something I might be able to shed more light on ask and hope I have the answer.

Dave ----

 

[Tyler]

Ok on PC now :nabble_anim_claps:What do they do on the FI trucks with dual tanks from the factory?I think the tank valve is switched by the fuel PSI IIRC and this also changes the gauge.I just don't know what that PSI is but why not do that set up on the truck?So you want to get everything for the rear tank like I think you said you got.Tank, straps, the cross member just in front of the tank the straps go to.As for the wiring. On my truck (81 F100) the dual tank wiring is all part of the main & frame harness.My parts truck was also a 81 F100 so it was just swap harnesses and I was good to go.Now I think you are using a newer dual tank harness in your truck so I don't know what you will run in to or have to make work.I think to go through all the work to have a level reading on the rear tank and have that pump transfer gas to the from is a lot of work.If me and I could not get both tanks to work like the factory did I would set up the rear 19 gal. as the main and the 16 gal. as the back up and transfer it to the rear.On the fill tube you are going to fill through the wheel opening?How much road dirt is going to be kicked up on it?Did you get all that from the parts truck?I like the clean factory look and why I molded the rear filler door into the fender.If you have a 2nd door assy. you could have a shop or you mount it in your bed side.I know not a lot of help here sorry.If there is something I might be able to shed more light on ask and hope I have the answer.Dave ----

I appreciate all the thought and feedback, Dave.I postponed the JY trip until I did more research.  No parts in hand just yet.

I might scrap the idea all together and just deal with having less gas and more stops...  I'm only going to drive the truck across country again once, LoL.

When I get back home to WA, it will be rare to take trips over 100 miles and the truck will not be driven much. It wouldn't be great to have all that fuel sitting there for prolonged periods of time.

I still like the idea of doing the "upgrade" though.

 

 

On Tue, Jan 5, 2021, 6:41 PM FuzzFace2 [via Bullnose Enthusiasts Forum] <redacted_email_address> wrote:

 

 

 

[Gary Lewis]

What about just going with a Bronco rear tank? They came in 28 - 33 gallon versions, but there are lots of 38 gallon tanks available. In fact, I have one that's new that I'm not going to use. I'd sell it for half price but the shipping might make the whole thing more expensive than buying one from a vendor that has good shipping rates.

A Bronco tank will fit our trucks, but you lose your spare tire spot.

[Tyler]

What about just going with a Bronco rear tank? They came in 28 - 33 gallon versions, but there are lots of 38 gallon tanks available. In fact, I have one that's new that I'm not going to use. I'd sell it for half price but the shipping might make the whole thing more expensive than buying one from a vendor that has good shipping rates.

A Bronco tank will fit our trucks, but you lose your spare tire spot.

Perhaps, I should focus on getting the truck running again before I undertake this adventure. I'll keep the Bronco tank in mind. The smaller of those is the most attractive to me.