Author Topic: Adding dual fuel tanks.  (Read 2795 times)

Offline Will B

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Adding dual fuel tanks.
« on: August 15, 2018, 09:14:20 AM »
Im going to be adding dual tank to my 83 K20. I was able to get a factory harness, switch and valve for under the cab. I have 2 tanks out of a late 70s trucks that I'll be putting in there. My questions are: 1) How bad is it going to be wiring wise? Especially plugging it into the fuse block on the fire wall? On both sending units they are 3 port. The center port on both was blocked off and not used. What is this port for? On the drivers side sending unit there is a electrical connection that went up to the front some where in the harness. Was this for the fuel gauge? My current gauge doesn't work but the previous owner wired in an aftermarket one. Any all all help and suggestions would be appreciated. I hate wiring so I'm leary about doing it.

Offline Henry

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Re: Adding dual fuel tanks.
« Reply #1 on: August 15, 2018, 11:35:30 AM »
Hi Will:
I cannot help you with the wiring...never done it myself. But I can tell you about the 3-port  tank sending units. On the 3-port sending units, one port is supply to the engine, one port is return from the fuel pump, and one port is vapor/vent  for the evap cannister. Your tank selector valve should have 6 ports, and these connections are all made at it. Early 70s dual tanks with heavy duty emissions had 2-port sending units and these worked with the 3-port selector valve.
Regards,
Henry

Offline Henry

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Re: Adding dual fuel tanks.
« Reply #2 on: August 15, 2018, 11:41:16 AM »
Hi Will:
I was in error on my last message...the vapor/vent lines from the tank sending units are tee'd together and then one line runs all the way up to the engine compartment to the evap cannister...they do not go to the fuel pump.
Regards,
Henry

Offline bd

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Re: Adding dual fuel tanks.
« Reply #3 on: August 15, 2018, 01:06:46 PM »
Except for potential maladies that may have been introduced by previous wiring "repairs," a factory tank selector harness should make the addition nearly plug-n-play.  See Fuel selector switch and the 1983 Wiring Manual for more details.

Reiterating, the fuel tank sender hose connections are:
3/8" = fuel supply from tank to pump
5/16" = fuel tank vent to vapor canister
1/4" = fuel return from fuel pump (application specific)

If the fuel pump has an application specific 1/4" hose nipple for fuel return to the tanks, plus the standard 3/8" fuel hose connection from the tanks and one 3/8" steel line running to the carburetor, the tank selector valve needs to have six hose connections, three 1/4" nipples and three 3/8" nipples.  If the application specific fuel return line to the fuel tanks is absent (only one 3/8" fuel supply hose and one 3/8" steel line are connected to the pump), the selector valve requires three hose connections, all 3/8". 
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Will B

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Re: Adding dual fuel tanks.
« Reply #4 on: August 23, 2018, 09:18:19 AM »
Except for potential maladies that may have been introduced by previous wiring "repairs," a factory tank selector harness should make the addition nearly plug-n-play.  See Fuel selector switch and the 1983 Wiring Manual for more details.

Reiterating, the fuel tank sender hose connections are:
3/8" = fuel supply from tank to pump
5/16" = fuel tank vent to vapor canister
1/4" = fuel return from fuel pump (application specific)

If the fuel pump has an application specific 1/4" hose nipple for fuel return to the tanks, plus the standard 3/8" fuel hose connection from the tanks and one 3/8" steel line running to the carburetor, the tank selector valve needs to have six hose connections, three 1/4" nipples and three 3/8" nipples.  If the application specific fuel return line to the fuel tanks is absent (only one 3/8" fuel supply hose and one 3/8" steel line are connected to the pump), the selector valve requires three hose connections, all 3/8".

I can't seem to get any of the drawings to show up in the link you shared of the electrical manuals.

Offline bd

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Re: Adding dual fuel tanks.
« Reply #5 on: August 23, 2018, 09:37:46 AM »
The manual is in PDF format, so you need Acrobat Reader or compatible software.  Depending on Internet download speed it can take a while to buffer and load.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)