Sorry, I know this has been covered but need a gut check at this point. I've googled everything I can about the dual tank selector valve and got some conflicting info so wanted to ask this:

1986 w/ 302 EFI and dual tanks
I have a dual function reservoir that is the later model design without the filter.
1. I have read that when no pump is running (truck off) the valve is spring loaded to switch to the front tank.
2. Conversely, I've also read that it switches and locks depending on what pump is running so both pumps need to be functioning properly for it to work right.
Is #1 correct?

More info:
Bought the truck as a surprise Christmas gift for my dad who would rather drive his beat to death '85 than his 2006 Supercrew. Been working on various repairs/pm's for the past few months to get it ready for him. Truck was running on front tank, was told rear was bad but that it was full of gas. Could switch to rear tank and truck would keep running. However, found tank was completely empty and had been dropped because lines were kinked, vent was knocked off, and rags were stuffed in filler neck. Figured since tank was empty the valve was not switching so the high pressure pump could still pull from the front tank.

Replaced rear tank, sending unit and pump assembly, tank vent, filler neck, and repaired lines. Existing selector valve on the truck was one of the later ones without the filter but I replaced it anyway to be sure it was good. Verified that the rear pump wiring functioned correctly (off/on/sending). Truck drove around fine and ran on either tank and I watched the fuel gauges to be sure both were moving down although I never fully filled it up until a couple of days ago.

Filled up both tanks, drove home on front tank, and parked for a couple of days. Yesterday I got the trailer to tow the truck 400 miles to dad and test loaded it (running on front tank), then put it back in the garage. Came out later and gas was dripping out of the rear tank filler, then came pouring out when the cap was removed. Assume the return fuel was going into the rear tank. Ran truck at idle on rear tank and let fuel level drop down some in filler neck. Capped both tanks and switched to front tank for a few minutes. Level did appear to creep back up in rear filler neck while running on front tank.

Now we're back to the start. If the selector valve switches to the front with no power on the rear pump I don't see how it could get gas to return to the rear tank (assuming a good valve). However, if that's not what happens I assume a weak front pump might cause the valve to only partially switch if it were cycled to the rear and back to the front.

I've already ordered a new front pump and sending unit assembly last night. You can imagine what a nightmare this is since I've been working on various repairs on the truck for the past few months, then to have this happen the day before I'm about to tow it 400 miles to surprise the old man. I'm having the pump sent to his house so hopefully it will arrive while I'm there although I'm dreading dealing with that full front tank.

Thanks for your time and patience reading this.

 

First - Your post was very thorough and well laid out. And, while long it was necessary to get the details conveyed. So no apologies needed. I like it and appreciate the time it took to do.

As for the valve, I don't know if it is supposed to switch back to the front position with no power, but I doubt it. If it did and the front tank were dry it would seem to cause a problem starting. So my bet is that it is supposed to stay in whatever mode it was left in.

But, I do know that it is entirely possible for the valve to pull from one tank and return to the other. Saw that on Ray's 1986 F150 w/a 302, which is why we removed the rear tank, valve, plumbing, etc. I assume after all the expense and work you don't want to do that, but since the valve does switch via pressure from the pump, it would seem likely that a weak pump could cause it to go part way. Have you tried switching it back and forth several times to try to loosen it up?

In any event, I applaud your efforts. I'm sure your father will be both surprised and pleased.

Oh - WELCOME TO FTE!

 

Hey Gary, thanks for the kind words and welcome.

Quick update....
Before I loaded it up this morning I went under it to see what tools I'd need to take with me to drop the front tank. Saw that the front tank's vent hose was pinched/crushed between the bed/frame and the sending unit. Backed the tank hanger strap bolts back enough to let it drop about a quarter inch and managed to free the hose. It's flattened, possibly torn, and I'll repair it when I get down to south GA.

Anyway, I switched back to the front tank, loaded the truck up, and then let it just idle for 30 minutes or so while loading other stuff up. Checked the rear tank level several times with a piece of marked welding rod and the level never seemed to come up any. However, it's in the 30's right now so the tanks aren't really getting hot and pressurizing so I don't want to sign off it as the problem. Also the level was lower than I left it last night by a couple of inches due to the cold. I reckon I'll patch that hose later, fill the rear tank up to almost overflowing, and then drive around some on the front tank to see if my Christmas present will be not having to drop the tank.

 

Good catch. With the vent closed the pump would eventually pull a vacuum on the tank and start losing output. That might allow the valve to partially close even if it is good. Sounds like a good possibility for the problem. Merry Christmas!!!

 

I know you probably did this already, but triple check the hose connections. A hose in the wrong place could cause this to happen(return hoses swapped). You could also disconnect both return hoses to the tanks, put short pieces of hose on and run them down into little containers, and get a better visual of what's going on.

 

Merry Christmas back atcha, Gary. Let's both pray that vent is the issue.

Dave, I'll check the hoses again but am pretty sure they're good especially since this morning it didn't raise any. The hoses are different sizes at the sending unit and selector, and one set turns up at 90 degrees at the selector so it's not easy to mix the upper and lower ports up....although I've done a lot worse.....

I'll be out of touch for a week or so. There's barely cell service at my father's house and they don't have internet or even cable TV.

Now here's the real kick in the rocks on this whole deal....Dad is 77 and has always wanted "straight pipes" on a truck but never had them. There's a place that makes some for this model BUT they won't fit with the rear tank and spare. The spare was already gone and I thought seriously about replumbing it for the front tank only and removing the rear. My problem is I hate having something on a car that is supposed to function but doesn't so I elected to "fix" the rear tank and just redid the exhaust with a high flow cat and y-pipe, and a 3" single exhaust.

Here's some pics of the truck once I finished with it. There are three pages of stuff I did to it and it still has some issues....main one is that leaking rear seal but I just convinced myself that it wasn't bad enough to pull the trans as I'd already drained the trans/converter for service and had the exhaust off once already. Another thing I shoulda done at the time....
http://flickr.com/gp/12176273@N05/380837/

 

Wow! That is one CLEAN truck! Even the dash isn't cracked. Is that a cover? I love it and I'm SURE he will. Well done.

 

Thanks man. Original dash! I don't think I've seen an uncracked one in 10 years or better. It's obviously been garaged. It did have several leaks in the cab from the rear seams at the rear window seal and from dried up seam sealer in the drip rails but I managed to fix all that, but I haven't found a speck of rust so it must not have been in the weather much. The paint took a good bit of buffing though.

Got down south at about 5pm (seven hours on the road, thanks Atlanta) and surprised Dad pretty good although he's the type that doesn't like anyone to spend a dime on him. We drove around about 20 minutes on the front tank and I stopped a few times to check the rear which never filled back up. Let's all hold hands and pray that it's whooped. Going to patch the vent line tomorrow and put some miles on it.

 

I'll bet your father is tickled PINK! That is one slick truck. You deserve lots of praise, but all I can do is give you reps. Maybe a pic of your dad and his new truck?

 

Thanks again, and also for the quick responses and help. I'll take some pics and put them up after Christmas.

 

Here's the bad spot out of the front tank vent hose. Drove around another half hour today and rear tank did not overflow.



And here's Old Blue.

 

I think Old Blue is fading away. He looks good in the first pic but is sorta faint in the next two. But the new one looks FAR better. I'll bet he loves it. And I'll bet that hose was your problem. Good job!

 

Yeah, trying to do this on a phone is very....trying.

Here's a not so pretty shot.

 

That certainly is a "not so pretty" shot. Rusted out floorboard, tattered seat, and missing door panel.

 

That floor looks eons better than mine. I have hole that spans from the rail to the hump in the center and the seat rides the frame rail. It's bad.