I've got a 77 F-150 with a 400, 2BB Motocraft Carb, and dual tanks.
I was on a cross state trip, and it was running fine, then it began puttering, as if it wasn't getting fuel, and died. A half hour later it started up and ran fine until I pulled off the highway and was in backed up city traffic. Once again, it began runnning rough and died. This time it was nearly an hour before it restarted. On the highway, perhaps 45 minutes later, it began puttering and died. I couldn't get it running this time around.

Thankfully, I was near my destination, and we pulled it to a friends house where I could wrench on it. The engine would turn over, but didn't seem to be getting gas. I pumped on the gas pedal, to an extent which would have usually flooded it, but I couldn't smell gas under the hood. I then replaced the fuel filters - the one that screws to the carb and the one after the fuel tank selector valve - and blew ot the line which runs between the carb and fuel pum with compressed air. It still wouldn't start, and I still couldn't smell gas.

Since fuel was reaching the filter that screws onto the carb, I figured it was a stuck float. I pulled the top end of the carb off, but things were looking good and seemed to work as well. I thuroughly cleaned the carb with cleaner and made sure everyhthing was working.

It started and ran, albeit rough, for a few minutes, before dying and refusing to restart.

I took it to a reputable shop and explained the problem to them. They replaced the fuel pump, which I really didn't think was the problem because it was only a year old and I had been running sporadically. It started and ran. I thought the problem was fixed, so I took her for a spin. Two or three miles later, it began sputtering when the engine was under load, although it idled fine in a parking lot. I rushed back to the shop and gave them hell.

The mechanic then began toying with the tank selector valve, theorizing that was where the problem was. He said "your front tank is empty. It's running off the rear tank that it's supposed to be on, but then, for some unknown reason, it's switching to the empty tank and dying". He ran the line straight off the rear tank, and suggested I drive it for the weekend ( it was Friday ); if there weren't any problems we would know that it was indeed the aformentioned valve and I could have them replace it for me.

It ran fine, so I bought a new valve and replaced it. When I went to the gas station I realized that I had over four gallons in the supposedly empty front tank. Hmmm. Whatever the case, I had a running truck, which was a welcom relief after two weeks without wheels.

But a few days later, when I was heading out on the return cross state trip, the problem arose again. It was idling/warming up fine, but when I took it out on the street it bogged down. I drove a few blocks before I decided that I better turn around and head home before it died. On the way back to the house it suddely came to life and ran fine. I made my nearly 300 mile drive without any problems, although I was totally stressed.

I reconnected the fuel tank selector valve and it ran fine off of both tanks. As it ran, I watched the fuel flow through the clear plastic filter that is between the fuel tank selector valve and the fuel pump. After awhile running off the rear tank (located above the trailer hitch) the fuel flow in the filter would decrease from 1/2 full to barely any fuel at all, the truck would begin running rough, and in time it would die. It didn't have the same problem off the behind the seat tank; I believe that this is because of the additional pressure provided from being located above the clear filter. I figured It would run fine off the front ( behind the seat ) tank as long as I kept it nearly full. Every time I would run it off the rear tank the fule level in the clear filter would be really low, it would bog down, and eventually die.

I replaced the lines connecting to the fuel tank selector valve, making sure they weren't kinked up, and checked all the other lines to see that they were in working order. After a week of watching the fuel through the clear plastic filter ever time I used the rig, it became apparent I was wrong. Although she won't run off the rear tank, as I've mentioned before, the fuel level in the clear plastic filter varies greatly despite the amount of gas in the front tank. Sometimes it's 1/2 to nearly 3/4 full, other times it's barely a trickle. It doesn't seem to matter how much gas is in either of the tanks.

I should note that I removed the gas caps as well, thinking that perhaps they were clogged and weren't allowing air to replace the gas extracted from the tank, to no avail.

I just don't get it!!! This is way beyond me and I can't afford to pay a mechanic $300 to not fix it again.

Please offer some suggestions fellas. Would a leak in the hard lines cause this/ these problems? No gas leaks from these lines, so how could I try to find a hole in them? Man, I don't know. Thanks for any help/suggestions. They're GREATLY appreciated.

 

That's a long post. Two things come to my mind. I know that a lot of people chase suppos'ed fuel problems only to find the old durafart ignition box is going sporadiacally south. Your post reads that you've been keepin' an eye on fuel flow via the clear view filter. I have a terrible problem with inacurate readings from my fuel gage....During my course of diagnosis I ended up pulling the sending unit. I was very suprised to find the plastic "sock" that pre-filters the fuel was disintegrating. Just touching it caused it to break off fibers. I inquired with my local FORD dealership about a new sock and the parts guy recommened (no replacement available) pulling the sock and installing an inline clear view like you have. I put mine before the pump in the engine bay and run with no "sock." Two years later and I've had no problems other than some rust that's made it through the fuel line only to be caught by the clear filter. Your "sock" on the rear tank may be clogged with rust or simply just blocking the flow of fuel. Dropping the tank to check the sending unit is a real bear, but it may give you some more insight to your problem.

 

If you have eliminated the possibility clogged up fuel filters & any leaks that would allow the pump to suck in air instead of drawing fuel,you might want to check to sock filter that is at the end of the pick-up which is in your fuel tank. If I'm reading you correctly you are saying that when you run off your front tank it runs fine correct? If this is true I'd check the back tank first.

 

This sounds eerily like a problem that I am having right now. Look for my post "I go away...I come back...I go away..." I have replaced fuel lines, fuel pump, carberator, cap, rotor, plugs, wires, and still I have the problem.

I just replaced the coil, hoping that is my problem. It seems like once the engine compartment gets to a certain temperature, it just loses power and eventually stalls out. I am usually able to get the truck started again if I pour gas in the carb, but the other day, even that didn't work. So now I'm on to the electrical system to find my gremlins.

Be sure to keep us posted on what you try, and what eventually solves the problem. I will also keep my post up to date with any progress I might make.

Good luck!

 

The most common heat related engine gremlin is the ignition module, next the distributor pickup module, and finally the coil.

Your method of checking the fuel filter level is a good one. There are several problems that can cause that variation in fuel level.

-A slight leak under vacuum in a fuel line that will allow air into the line when a vacuum is applied. A manifold vacuum and fuel pressure test gage will show that problem if you block off the lines at the tanks and apply a vacuum with the fuel pump or a vac tester. A test gage will show this problem also.

-A clogged fuel tank "sock". Either clogged from debris or rust. I like to eliminate the sock and use a piece of rubber hose with notches cut in the side to allow multiple points for fuel entry and then use an inline filter.

-Heat from the engine can vapor lock the pump. Adding insulation to the fuel lines and/or installing a fuel bypass at the carb with a return line to the tank. This helps bring in fresh cool fuel to the carb and also filters the fuel in the tank. This works like a bypass fuel pressure regulator on an EFI setup. The bypass is a tee at the carb with an insert with a small orifice in the return line back to the tank. This lowers your fuel pressure slightly under high demand situations but is self compensating also. You will need an EFI type selector valve with a valve for the return line.

-An inoperative fuel tank vent, which you have eliminated by removing the caps.

 

Thanks alot for the suggestions fellas; please keep 'em coming.

I'm fairly sure the problem is with the fuel system and not anything electrical.

I wasn't aware of a "sock" in the fuel tank. I suppose it's time to check it out. What is the sock? Where is it located? What's the best way to go about checking it? Given my luck as of late, it's most likely pretty labor intensive.

I don't mind doing the work myself, in fact I'd rather do it that way in order to learn more about my truck and to save on steep shop costs, but messing with the fuel system has been a real mess. I'm tired of being covered in gasoline, not to mention the offensive smell that flows thru the neighborhood, and the unlikely risk of a fire. Hmmm.

Thanks again guys.

 

I had a "sock" problem in a '65 Caddy on a Canada fishing trip... I was lucky enough to stop at a small garage and the old boy there disconnected the line on the tank side of the pump and blew air back through the tank...I almost made it home but when it would seem like it was running out of gas , I would blow it out with lung power and it would be good for another couple hundred miles...No more sock filters for me...

 

The sock is a nylon mesh screen that is cylindrical in shape about an inch and a half in length and has a diameter about the size of a nickel. It is attached to the end of the fuel pickup. You'll have to drop the tank to get the pickup / sending unit out. Mark the orientation with a marker prior to disengaging the lock ring - that way you can reinstall it in the correct position. I was able to simply pull the sock of the pickup...most of it crumbled when I did so. Don't forget to unplug the wires prior to dropping the tank. I think the worst part is getting the stinkin' filler and vent hose back on when you re-install. Round hose through a rectangular slot....not Ford's finest hour ;(

 

If you eliminate the "sock" in the tank, install a filter in-line ahead of the fuel pump to protect it from any debris that might pass through the tank.

 

i think if i dropped the tank like that i might just take the time to reseal the tank with like POR-15 Rust Inhibitor.. The stuff works wonders..

 

It looks like I'll be removing the socks and perhaps sealing the tanks this weekend. I'm keeping my fingers crossed that this'll thake care of my problem.

The problem now is figuring out how to drain the nearly 18 gallons in the rear tank and the 10? gallons left in the front tank.

Thanks again