Gents,

I have a 78 F250 Camper Special 4x2 with dual tanks. replaced both tanks, new floats and seals. Main gas tank works fine. The issue is the rear tank. The selector **** on the dash works fine, shows proper capacity in the tank, however, I am certain that the gas does not pump from the rear. Everything is plugged in, all wires are working, it is grounded on the frame, but no gas flows from the tank.

I ran out of gas last night when I thought I was running off the back tank. The tank showed 1/4 full (and it is) but I must have been sucking the main tank dry, while never actually running off the rear tank.

How do I know if the rear tank is actually pumping gas to the engine, carb, etc...? Do I have a fuel line problem? Is it a sending unit problem, a fuel pum issue?

 

My truck did this also .... turned out to be a crack in the fuel line between the tank and the switch valve. Instead of getting gas it sucked air, lost its prime, and then quite once the residual gas was burnt by the engine. If this is not the problem maybe check to see if your rear tank fuel line got air locked.

 

thanks, I will check that tonight.

Is there any other electrical connections that I am missing?

 

not sure about that; my 73 is all manual switch from tank to tank --- bet Mil1ion could answer that if you PM him

 

On my '76 F250 SC the main tank is in the rear between the frame rails, and the aux tank is the midship mounted tank. Yours is this way too or it should be unless you fed them backwards at the switching valve. So are you sure you are working with the right tank? I've read of problems where the valve will suck from both tanks. You could isolate one tank with a fuel line tool made to pinch the line shut and see if you are able to run on each tank separately. That'll also help you figure which is main and which is aux if you are not sure.

 

Tractoman is correct. Rear aft-of-axle fuel tank is the MAIN, and REAR. Always! Single tank trucks are set up the same. The FRONT, the gas cap/door being closer to the cab, is always AUX. If you have indeed isolated the problem to the rear tank (aft-of-axle) then check for the fuel hoses, pickup screen being clogged, solenoid value.

The tanks are the constant fed system variety so you will always have some gas in either tank. Anything less than three gallons in the REAR/MAIN tank will not able to get pumped effectively.

 

 

This has been discussed before in here.And contrary to what some other members have said/In a trk with dual tanks the FRONT tank is considered the Main tank on the switch and the AUX is the tank behind the rear axle.It says as much in your owners manuel if you have one.It seems like unconventinal thinking on fords part,but that's the way they set it up Regards

 

No, it is not.

STRAIGHT from my Owner's Manual:

"If your vehicle is equipped with dual fuel tanks, the level in either tank may be checked by reading the fuel gauge with the fuel selector switch in the desired position. This switch also controls the fuel flow from either tank to the engine. The fuel valve is energized when the fuel selector switch is moved from FRONT to REAR position, allowing fuel flow from the rear tank. On vehicles equipped with dual fuel tanks, the FRONT position supplies fuel to the engine from the midship fuel tank. The fuel valve is protected by the fuse label "AUX TANK SOLENOID" on the fuse panel."

 

I don't know about that. On my 77 the rear tank is MAIN and the front tank is AUX. However on my dad's 78 CS the rear tank is AUX and the front is MAIN. So I really don't know?!?

 

Yes it is
On page 9 of the original owners manuel my Lariat came with (brown book 1978 0wners manuel for f100 thru f350 series printed NOV 1977 2nd printing part # d8TA-19A32-BD) It states

The fuel valve is energized when the fuel selector switch is moved from MAIN to AUX position,allowing fuel flow from the auxiliary tank.On vehicles equipped with duel fuel tanks,the ""MAIN"" position supplies fuel to the engine from the midship fuel tank.

It also provides a diagram AUX up Main down for switch I agree conventional wisdom would say that since all our trucks of that era had at least the rear tank and the front or mid-ship tank was a option that the rear would be considered the main tank.That however is not the case.As stated above by the manuel the rear tank in a dual setup is called the AUX and the mid ship is considered the Main

 

Well no matter what the tank is called the poor guy isn't getting fuel from it so maybe we all better get focused and do what this website does best ---- HELP FORD TRUCK OWNERS GET THE MOST ENJOYMENT THEY CAN FROM THEIR TRUCKS.....

 

sorry, I don't think Ford was that stupid to put a MID-ship tank that causes the weight of 19 Gallons of fuel to be on one side of the frame as a Main Tank.

The Rear fuel tank which is not weight sensitive for truck weight balance is thr MAIN Tank.

The Photo I posted above shows the way Ford identifies it .

My 78 says

Aux
Main



Aux = Mid-ship

Main = Rear between frame


This photo is of my truck

From the factory.... no alterations have been made.
with the switch in this position..fuel is being take from the "Aux" MID-ship tank.

 

Guys,

you all know more than me for sure. I can tell you that the midship tank is the first door towards the cab, the second door is the aft axel tank. I know this for sure, I installed them myself and mirrored what was present at the time. When the switch is in the downward position, that is the midship tank, when the tank is in the up position, that is the rear tank. I can tell you that there maybe less than 3 gallons of gas in the rear tank, this may be the issue. I am going to fill up the back tank tonight and see what happens.

Thanks and sorry for starting a mini war.

Western Star is right and I will follow his mentality.

Mike

 

All I can add to this discussion of main and aux and position of switch. I bought my 1975 F250 S/C new, and my switch on main is rear tank and on aux it is the mid tank.