1975 F250 4x4, 360 automatic, unmolested original with 62K miles and the stock in-cab tank.
Trying to figure out a strange fuel issue.
This truck is new to me and I am trying to get it to a reliable daily driver.

Two times it has left me stranded on side of road; fuel gauge reading just under 3/4 full and both times just adding gas has gotten it running again.

BUT when filling it up immediately afterwards, it only takes between 5 and 7 gallons to get to full(and gauge reads full)
This leads me to believe that the fuel gauge is indeed accurate; I have been in touch with the previous (original) owner and he states the gauge is accurate down to empty.

First time it "ran out" of gas, I added 1 gallon on side of road and it only took 7 additional gallons to fill.
I also replaced the ignition module as I have read those can go bad with similar symptoms and I also replaced the fuel pump as it was leaking.

Today it "ran out" I added four gallons of gas on side of road and it fired right up. Drove immediately to gas station( 1/2 mile away) and filled tank with only 5 gallons more.

So it seems I have about an 8 or 9 gallon usable in-cab tank.
What should I be looking into(beside carrying a 5 gallon Gerry can) that would reduce my 18 to 19 gallon tank down to about half of that??

Thanks in advance
Tbruz

 

Sounds like a pressure issue with the tank. DO you ever smell gas in the cab when driving it?

 

No fuel smell in cab
Thanks
Tbruz

 

Check all fuel filters? Especially the suction side if there is one. Sometimes they clog under load and then 'relax' when there is no flow. Almost sound like your tank is pulling a vacuum.

 

I had an issue with old rubber fuel lines getting soft and sucked shut by the pump. The truck would die, wait a while and it would re-start and run a bit then die again. In your case, the time spent adding the gas may have let it recover or the slightly higher pressure with more gas in the tank helped resist collapse of the fuel line.

Suggest you inspect/replace all short sections of rubber fuel line, especially on the suction side of the pump.

 

could this be a standard "vented vs non vented fuel cap issue"? Sounds like he is using a non vented fuel cap and needs a vented one.

When you "run out of gas", does it feel like the tank is under suction when you remove the cap? does it make a whooshing sound as air flows into the tank? if so, get a vented cap. Next time it runs out, simply loosen the cap, wait a minute, then try to start it. If it starts without adding gas, then the problem points to the cap or fuel hose described above

 

Evaporative Emission (Evap/Em) System: Unleaded fuel, non vented fuel cap.

Evap/Em fuel tank has a vapor valve, line runs from vapor valve along inner right frame rail to the charcoal canister under the hood. If two tanks, there are two valves, two lines.

The non vented Evap/Em fuel cap has 4 prongs, 2 above, 2 below 180 degrees apart. The fuel filler tube has a restrictor inside it that only allows an unleaded fuel gas station nozzle to fit in.

Back then, there were two different gas station nozzles, the one used with unleaded fuel was smaller in diameter than the leaded fuel nozzle.

But, what some people did was, they knocked the restrictor from the filler tube so they could use leaded fuel. Sometimes they replaced the non vented cap with a vented cap.
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
The fuel tank sending unit float is made of two pieces of copper soldered together. Solder breaks down, gas seeps in, float begins settling towards the bottom of the tank.

COAZ-9202-B (replaced COAZ-9202-A & B7A-9202-A) .. Fuel Sending Unit Float / Available from Ford ~ MSRP: $27.76.

Applications: ALL 1957/79 Passenger Cars/Trucks; 1961/79 Econolines & 1966/79 Bronco's.

Carpenter sells a similar float for around 5 bucks.

 

84Espy
Only one fuel filter on this truck and its part of the fuel pump which was replaced after the first "run out" incident due to leaking and my thinking it was weak. No filter at base of carb or inline elsewhere

Blue and white
I do see two short pieces of fuel line will replace those and advise back

Jklnhyd
I have a short neck fuel cap with only two prongs, 180 degrees apart, I think its vented as I do not hear a "whoosh" when opening. I have a longer neck cap with 4 prongs, 2 above and 2 below 180 degrees apart, but it does not secure to the filler neck, It just keeps spinning around

Number Dummy
I believe I have a non-Evap system; there is no nozzle restrictor in the filler neck and the actual tank has the opening for the filler neck, the sending unit and fuel feed line, thats it, no other bungs or plugs or tubes; original owner says it was never replaced.

Truck has a second saddle fuel tank.All the plumbing from the switch forward to the engine is common to both tanks
I am currently running it off of that side tank and will see if I get more that 9 gallons of distance before I "run out of gas" again. I'll keep the in cab tank as my reserve until I/we figure this out

If I do get more distance from side tank then the issue has to be switch back to the main tank( in cab tank or its line)

All good ideas keep them coming....
Thanks
Tbuz

 

Do you hear any air whoosing when you remove the cap? That would indicate a lack of venting.

 

No whooshing sound heard when removing gas cap.
Thanks
Tbruz

 

Replace the $4 fuel filter and see what happens. NAPA or Advance should have them in stock in various sizes. When they start restricting flow you can drive easy for long distances but if you try and go up a hill or something and really start sucking down the fuel it won't let enough get through and you use all the fuel in the carb bowls. Leave it sit for a few minutes and it will fire right back up and get on your merry way...until you need lots of fuel again.

 

I had the same problem in the 64. It would "run out" of gas with about a half tank. Never did figure it out, exactly. It was either a weak fuel pump or it was sucking air past a portion of rubber hose? If the fuel pump is old it's not a bad plan to replace it on GP.

For sure replace all fuel hose and clamps, there is a short hank of rubber under the cab, too. The "brake line" sold at auto parts stores bends up nicely to recreate the OEM fuel line. Rubber fuel hose is not a good idea these days.

Blow out hard lines with compressed air. Re-set carb float level. I even replaced the fuel tank as I was certain the fuel tank pickup tube "had to be" rusted out or had a pinhole. Maybe it did, I dunno.

 

I had decided to replace the gas cap with a new NON EEC one from LMC for $6.95 but then pulled the carb off for a rebuild and so I got sidetracked on the "running out of fuel issue".
Finally got the carb back on and went for a good long ride, beyond my previous 7 gallon range. Fuel gauge reads below half now where before it would "run out" between half and three quarters full.

Preliminary results look like the issue was the gas cap, nice cheap easy fix.
Thanks all,
Tbruz

 

Thought I'd gotten this issue fixed with the cap replacement as I had previously reported BUT.....
The issue continued, not on every tank full but frequently enough to be a pain in the a$$ and make me question the reliability of the truck.
I overcame/compensated for the issue by swapping over to the second tank each time I would run out" of fuel and the truck would start up again.
Today I got motivated and fuel level was low enough so.....
Look what I found in the tank: look like the seals inside the caps of fuel additive/dry gas.
These must have been randomly blocking off my fuel flow and the truck would "run out" of fuel. Running on the second tank would start the flow and these float around again until getting sucked down/sucked over to block the flow again.
Will fill up in the am and go for a ride; hopefully I really do have the fix now.
Thanks
Tbruz

 

Interesting. That could be it. Course it might not be, too. Let us know what you find.