debugging dual tanks
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Mountain Pass
Joined: Sep 2000
Posts: 233
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From: Eagle River, Ak
debugging dual tanks
My '78 Crew cab has dual tanks, but only the rear works.
(The rear is the main tank and the front is aux right?)
I am assuming both tanks connect to a switch and the switch has an output to the fuel pump? Is that correct?
Any hints on solving this, common points?
Thanks,
(The rear is the main tank and the front is aux right?)
I am assuming both tanks connect to a switch and the switch has an output to the fuel pump? Is that correct?
Any hints on solving this, common points?
Thanks,
Lead Driver
Joined: Mar 2004
Posts: 8,922
Likes: 152
Not on my '79 f-250 4x4 & the fuel gage verifies that. I think with more research you'd find out they changed that at some point. If your getting power I'd try a new solinoid.
Last edited by mark a.; Mar 14, 2005 at 09:07 AM.
Lead Driver
Joined: Mar 2004
Posts: 8,922
Likes: 152
Forgot to ask is your gage working in both positions? If so & the power is working to the solinoid, then the valve in the solinoid is probably stuck / corroded in place. Any new ones I have found from Ford or after market have 5/16" fittings, but will work. You just have to clamp them down harder, mine hasn't leaked at all. yet.
Post Fiend
Joined: Jul 2003
Posts: 11,945
Likes: 3
From: Spokane, WA
Originally Posted by Mil1ion
Sorry Mark, The rear tank between the frame is considered the main tank.
Laughing Gas
Joined: Apr 2002
Posts: 869
Likes: 1
From: Apple Valley CA USA
On a 73-79 Ford truck with dual tanks the midship tank is the main tank except for a few models that had in cab tanks instead or rear frame tanks. If the switch and control read backwards from this it is simply because the wires and hoses were swapped. It is extremely easy to switch the wires and is done even by dealers who install a new fuel valve and hook the two tank hoses up backwards. It is easier to switch the two plugs on the dash switch than it is to fix the hoses correctly. It is very common to find this. My owners manual does note that the midship tank is the main tank (but of course mine has an in cab tank and so its wrong! LOL). Hawkrod
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New User
Joined: Jan 2008
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Oh Great, thanks Ford 
On my switch, in the Up position it draws fuel from the main (Rear) Tank
Down position > the Front/side Aux tank.
All the owners manual says is :
IF a frame mounted front tank is installed,the filler is located on the driver's side of the vehicle,behind the cab on the side panel;on Crew cabs the front tank is just behind the left hand rear door.
I still think the rear tank is the MAIN tank.
Why would they think different, (reverse their design) just because the truck now has two tanks?
I just looked in the small 1/2" thick spec's book that is number #7 in the set & in there is a listing of numerous set-ups but they still refer the aft axle tank as the standard main tank.
It's called the RPO Tank listing.
On my switch, in the Up position it draws fuel from the main (Rear) Tank
Down position > the Front/side Aux tank.
All the owners manual says is :
IF a frame mounted front tank is installed,the filler is located on the driver's side of the vehicle,behind the cab on the side panel;on Crew cabs the front tank is just behind the left hand rear door.
I still think the rear tank is the MAIN tank.
Why would they think different, (reverse their design) just because the truck now has two tanks?
I just looked in the small 1/2" thick spec's book that is number #7 in the set & in there is a listing of numerous set-ups but they still refer the aft axle tank as the standard main tank.
It's called the RPO Tank listing.
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Thread Starter
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Mountain Pass
Joined: Sep 2000
Posts: 233
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From: Eagle River, Ak
Last time I drove with it on AUX and when I filled up the front take is the only one that needed gas.
The rear was very full, I coul see some gas in teh filler, so I switched it to main, drive down to the next exit and back through town. Now I can not see any gas in the filler.
So maybe it is working.
Now I just need to figure out the gauges.
The rear was very full, I coul see some gas in teh filler, so I switched it to main, drive down to the next exit and back through town. Now I can not see any gas in the filler.
So maybe it is working.
Now I just need to figure out the gauges.
Thread Starter
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Mountain Pass
Joined: Sep 2000
Posts: 233
Likes: 0
From: Eagle River, Ak
I forgot my excuse!
When I gto the trucks I was told both tanks did nor work in this one.
Apparently I was told wrong and it is the parts truck with the problem, which really is no problem...
When I gto the trucks I was told both tanks did nor work in this one.
Apparently I was told wrong and it is the parts truck with the problem, which really is no problem...
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