Gas tank port is 3.5" inside Dia the middle of the gasket groove is 4.375"

 

If it wasn't for bad luck. I wouldn't have any at all.
finally got it to seal, had to hammer down the locking tabs. Went to test it and noticed some wetness at the back of the tank near the seam. Tank has a pin hole. Just going to order a new tank.

 

New tank installed, had a heck of a time pushing the locking ring down enough to get it to catch.
I took it to the gas station I put 20 in each tank...lol, gas is expensive still $4.60 a gallon here. I did notice on the front tank when I opened it that there was a vacuum on it, is that because of those check valves?

 

I am not sure why you would have vacuum when you take the cap off. My single tank has never had vacuum or pressure on it. The black rubber fitting for the tank is for the roll over valve? doesn't it also have a rubber hose that runs over to a line running up the frame rail to the carbon canister?. You have 2 tanks so I'm not sure how those route without looking it up.. I am trying to remember how that roll over valve works.. I believe it is open when the van is in the upright position allowing fuel vapor to vent to the charcoal canister. If the van wheels are facing upwards,,,, then the valve closes so stop fuel from draining out. If I had my 85 van up here I could check that for us because its new tank is inside the van.

The new tank looks nice and I hope that finally fixes your issue! I would be so over dropping tanks by now, you must have really great patience!

Since that fuel tank selector valve can no longer be found unless you buy a Chinese brand like the first one you had trouble with, something is going to have to be redesigned.
My single tank van is fairly simple. If I wanted to carry more fuel then perhaps instead of plumbing it in with a selector valve, I could just add a side tank and use the in tank pump in that side tank to refill the rear tank that I run on now. I believe the side tank is 16 gallons and the rear tank is 19? For safety perhaps one could add a keyed switch so that the side tank pump could only be operated with the key in and on. That way you wouldn't be able to accidentally fill the rear tank unless you meant to. Ideally you would want a float switch..

Another thought might be to check into using a newer style selector valve used in the newer trucks but I am not sure how that valve works. I believe the newer trucks do not use a frame mounted pump, the pumps are high pressure and in each tank and there is a module that controls the selector valve. You would still need to plumb in a single reservoir though.
The new valves look like this
https://orionmotortech.com/products/...BoCjtIQAvD_BwE


Just some thoughts

 

Thanks for the thoughts Annaleigh, I'm really not sure if it's pressure or vacuum either, I'll be heading to the gas station this weekend to put more gas in the tanks and buy a new battery so I'll try to figure that out. I always assumed that if there was vacuum or pressure, the one of the vent lines had a blockage, that's another thing I should have looked at while it was down, but that's hindsight LOL. So far the worst thing about dropping the rear tanks is removing the filler neck lines, just not a whole lot of working room for your hands.

The aux tank is a good idea, kind of like the one I use to carry in the back of my truck, just flip the switch and transfer to the main tank.

If these check valves don't work, and I have no reason to believe they wouldn't, I may just separate the two tanks completely install a shutoff valve on each supply line. I haven't fully thought it out yet, but there has to be a simplified way to isolate each tank so they can't flow to each other.

With winter coming on I don't know how much more work I'll get in on the Van this year, but this weekend will be a good shakeout test to see if it's going to be a fairly dependable vehicle for so road tripping. There's still a couple of Van-ins I'd like to do this year up in Michigan and I think Indiana, and then there's the trip to Mississippi, that one is about 1200 miles round trip, One thing I know for sure is to make sure my insurance is still has towing on it and make sure my credit card limit has enough room on it to handle repairs if I breakdown on the road....LOLOL

 

The fuel caps on the pre 1996 models are vented roughly .060 size hole
Not sure whether the one way valves have any effect on the furl tank pressure and the vacuum on the cap when removed
Good luck on it Mike and hopefully you still have 2 working fuel tanks when you get back to working on it
Look for a new crossover valve just for GP's
At least the van ones are still available I believe

 

I've been thinking about this, I put that front tank up pretty tight to the floor, I almost wonder if a hose moved and maybe I pinched it closed because it wasn't doing it before I lowered it and add the chk valve. This weekend, I'll lower the front a little and make sure all the hoses are where they're suppose to be.

 

Well I'm back......I guess I still have a fuel problem, I ran the rear tank down to about 1/8th tank, went to get gas in the front tank, I put 11 gallons in it. Brought it to just under full, drove about 6 miles, looked at gauge and I was under 1/2 tank. I flipped over to the rear tank and it's right about 1/2 tank, so I can only assume the front tank is now back feeding into the rear tank through the return lines....any thoughts on the next direction to go?

 

What would happen if the return lines got swapped at the switch valve? Would it cause fuel to flow from on tank to the other?

 

You might be able to hook it up wrong, but its a common sign of a faulty switch.

 

When you say switch you mean the mechanical valve and not the actual switch?
As for the valve, this is the 2nd one. I just Cleaned up the original Ford valve. The plungers were jammed, everything works now, i guess i can try re-installing it and seecwhat happens. My only other option would be to run only the rear tank or put on an after market electric switch valve.

 

Did you get the hoses exactly where they come off, so many have done this, saw a van near me, wasn't running, said wasn't getting gas, had dual tanks so I avoided it.

 

Well I thought I did put them back exactly but I didn't take pictures or draw diagrams....lol

 

Here is some info and short comments that might help out

First after all of the problems I have seen here on duel tanks, i think that we have to start thinking of a way to redesign the factory system since we can no longer buy a Ford valve and the Chinese ones seem to not last.

First I would go to a single rear tank using this reservoir to replace the duel tank valve. I am thinking that it should bolt right up in the same place.

first is the duel tank valve to compare to the single one.





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When I had mine apart there is a blackflow valve built into the valve. you can see the spring up inside the hole. Not having a duel tank reservoir in front of me, I presume it too has backflow a valve in it. the duel. I have a exploded vies pic of the duel valve somewhere and will post it when i find it. In this pic of a single tank reservoir, the backflow valve is under the fuel tank supply line inlet connector. I am not sure what the meaning of the blue stripe is but the fuel supply line from the tank is sleeved with a foam sheath that has that blue stripe. It's raining right now or I would go out and look at the return lines to see if they are marked in any way.

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When it comes to fuel lines. The fuel supply line from the tank and to the HP pump are a larger diameter then the return lines. Again I presume that the same is true on a duel tank reservoir switch valve, fuel supply lines are larger then the return line.

How are the lines routed? This is from an 88 and the best pic i have for routing. You can blow this pic up and along with the work you have done should be able to remember these line pretty well by now! If they are the same as on an 88.





I am not an engineer but one would need to think about safety first. if they used the 22 gallon rear tank as the main tank and the midship 16 gallon tank as a storage tank to pump fuel into the rear tank when needed. Using the single tank reservoir shown above then it would be connected just like a factory single tank van.
You already have the fuel door to fill the midship tank at the pump and it too is connected to the EVAP system. So howto move the fuel from the midships tank to the rear tank?

https://www.whitmancontrols.com/l40-...kaAqikEALw_wcB

Above is a pic of a magnetic float switch, one of many that is gasoline rated, If one installed a normally open switch (when the float was at the top), That could be used to shut off power to the midship tank pump when the rear tank was full.
Since the van wiring was set up to run one HP pump and one in tank pump together, I would think one would need a separate circuit to the midship tank that is controlled by dash switch going to a relay with the float switch tied into that circuit. So you see the rear tank is low and you flip transfer switch on the dash. The relay is energized and the pump energizes and starts pumping fuel to the rear tank until the float switch activates and shuts the pump off through the relay. You would always be able to check the fuel level with the gauge in either tank.

From your new transfer tank, would you tee the supply into the return line to the rear tank or have a shop weld in a ford fuel line connector into the rear tank or on the sending unit plate?

Those were just some very basic thoughts.

 

Annaleigh , interesting thoughts. My fuel system is fully functional, both tanks work. I put the check valve on the supply side on both tanks which didn't work obviously. So I am assuming at this point I either crossed return lines and front is siphoning to rear or the check valve on the front pump assembly is bad or the mechanical switch valve is not fully opening and closing allowing front to fill rear. I could easily install an electric transfer pump into the front tank line sending to the rear tank. I kind of wanted to stay stock as possible, but it will probably come down to using just the rear tank and keep the front to transfer over.
thank you for your input.