Dear fellow enthusiasts,

I recently acquired a 1983 F-250 regular cab with one previous owner and a known issue...the engine heaving for gas once it dropped to the half-tank mark.

Both fuel pump and fuel filter had been recently changed, among other small maintenance adjustments including new sparks and wires. In driving it down from the mountains following the vehicle transfer, the engine completely died at half tank. I then poured 2 spare gallons into the tank and it started up and finished the journey home.

I'm perplexed. How is it that it can run fine at full tank, but upon reaching half it begins to sporadically shudder, as if not getting enough gas?

Thanks for any thoughts.

 

Key info - how big is the tank? If you have a sender/pickup for a 19 gallon tank in an aftermarket 38 gallon tank, that could do it. If you have no venting in the tank and an unvented cap, it will run only until you drain enough gas from the tank to where you effectively have a vacuum (easy way to check - when the engine dies, take the gas cap off - if there is a big whoosh of air into the tank, there you go. It should restart afterwards, and run until you drop the air pressure too much again.) Third option the pickup tube in the tank may have issues and halfway up may be broken or cracked wide enough to start sucking air instead of liquid. I'm sure there are others but that should at least get you started..

 

When "empty" at half tank, fill up the tank and see how many gallons it takes. The gauge may be reading incorrectly.

 

Plus if you do that it postpones having to pull the tank to check the other stuff!

 

Thanks 1986F150six. I can add 8 or 9 gallons when at half, and according to the previous owner, the gauge is reliable until a quarter tank, so I'm led to believe I've still plenty of fuel in the tank (19gal tank).

@HoustonDave...I just inspected the gas cap...no sign of air pressure difference and the truck still would not run more than a half second or so (I ran it down to half tank to troubleshoot the issue). My hunch was initially an air exposure in the line somewhere that was effected by fuel level, so you might be onto something with the pickup tube.

 

Hello brennadon, and welcome to the forums.

HousonDave basically said the same things I was thinking.

A hole in the tube on the sending unit inside the gas tank. When the gas gets below a certain point, the hole becomes exposed and your fuel pump starts sucking air as well as gas.

Your gas tank isn't venting at all, so when your fuel drops below a certain point, the large cavity in the tank creates such a strong vacuum that it overpowers the fuel pump.

Either way, it seems like something to do with the tank since it's always at a specific fuel level.

 

It's a bad sending unit or the float is broken causing a false reading. I have a broken float in my rear tank and it reads "E" when in reality I have between 1/4 and 1/2 in the tank.

 

Think I would disagree with that diagnosis, he is pretty specific that when he runs into problems is indeed at about a half-tank of gas so the reading is accurate. Given that the pickup tube is part of the fuel sender though, we're both saying it's a bad sending unit.
Given that he has a little tank (19 gallon) the good part is that the tank is pretty easy to drop and the sending unit is pretty cheap.