1977stepside

I have a 1977 f150 with a 400. Truck has run great with no issues for the last year or so other than a fuel pump going out which I replaced.

Lately it has started randomly stalling out and dying. Sometimes I can keep it from dying by giving it lots of gas.

If it dies, it won't start unless it sits for a day or so. Then it starts up with no issues.

It's difficult to diagnose because everytime I go to work on it, it magically has fixed itself.

Things I've figured out so far:
1. Gas tank seems involved in some way. The stalling and dying seem to happen usually right after I remove the gas cap (usually after getting gas)
Also, when I remove the gas cap it releases a tremendous amount of pressure with a woosh.
2. When truck dies, removing the hose before the carburetor shows no fuel being pumped through.

3. Fuel pump was replaced again, fuel filter was replaced, and air was blown back through the fuel line into the tank. This was done to potentially blow off the lining sock in the fuel tank.

An inline fuel filter was put in before the fuel pump to prevent any debris in the tank from passing through.

After installing the above yesterday, it seemed to be running great. Drove it all over and drove it again all day today. However, after I stopped to get gas, it ended up stalling and finally dying on me.

I have no idea what to do next. Anyone ever experience anything similar or have any ideas? I'm new to the forum and couldn't find anything in the other threads. Thanks!

Matthew Burr

fuel tanks are designed to contain the fuel, but also allow them to breath air in and out. if you try to pump fuel out of a steel container you will create a vacuum that prevents any more fuel from leaving once you reach the maximum pressure the pump can create.

you shouldnt have an excess of pressure in your tank or a lack of pressure. so i would double check if you have anything forcing air into your tank, usually theres a line that pops up under the hood on the passenger side connected to a carbon canister. if your pushing air into your tank faster than the pump can pull it out it may be causing a backup inside the carb.

i'm not 100% on this but thats what i where i would start looking. carbon canisters do go bad, and if just leaving the vent open to air fixes the issue then you've localized it.

GhostriderI

First off Welcome to the site

And to add that line goes to a vent on the tank (my tank it is centered aft of the sending unit about 6") It has a plastic floating ball to prevent fuel from flowing to the carbon filter during refueling, if the ball gets stuck in the closed position it will allow a vacuum to be created in the tank until it frees itself, then run normally (drove me nuts when I filled the tank full, no problem if I never filled full)
Where is your fuel tank mounted? Behind seat, side mount( between cab and rear wheel), or rear (behind rear wheel) Next thought have you replaced the fuel cap? if you have/do make sure to get the correct one. There is one for non-ECC and one with EEC (Evaporative Emission control) I think the difference is vented or non vented fuel cap.

Hope this helps

1977stepside

Thanks! I'm having some trouble determining which kind of tank I have. I can't find any evidence of a charcoal canister or venting system and the original gas cap was ventilated. At one point I did install the wrong gas cap but recently replaced it with a venting one.

The stalling problem seems related to me taking off the cap but it still continues to have problems with the gas cap off. A really frustrating situation. I'll look into the float and see if that's the problem.

The tank is rear mounted.

GhostriderI

Item 3 and maybe 4 depending on the age of yours

http://www.lmctruck.com/icatalog/FC/full.aspx?Page=31

Hope this helps

GhostriderI

Another thought you stated when you blew air back into the tank through the sending unit it ran good for a while. Have you dropped and cleaned/inspected the tank if it is the original there could be 30+ years of trash in the bottom tank and every time you refuel you stir it up. Just a thought

1977stepside

Thanks for all the help so far. I'm going to drop the tank this week and get it cleaned out.

Another thing to note is that if I blow really hard into the gas tank I can get some gas to flow to where the fuel line connects to the fuel pump.

Today the truck won't start even after sitting and blowing fuel to the fuel pump. The fuel line before the carb is completely dry.

Hopefully dropping the fuel tank will give more insight to the situation.

GhostriderI

If your pickup tube on the sending unit is plugged/has pinhole , or there is pinhole in the hose you will only suck air. I had an old car that would idle but never get above 30mph with foot to floor it was a bad piece of tubing at the tank. My father let me replace the fuel filter, pump, and carb. before he "suggested" I check the tube. I wondered why every time I went to get a part he would ask "are you sure" before we went to the parts store. looking back I think he knew all along and wanted me to figure it out for myself. I was younger then