4.9L 300 engine gasps for gas at half tank, 1983 F-250 Explorer

ford
explorer
f250

#1

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. Prior to arriving home, I filled the tank completely and it only took 6 more gallons (19gal tank). So this doesn’t seem to be an issue of a fuel gauge malfunction.

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? If I continue to run the truck beyond half, it will stall or not start at all. Put a couple more gallons in, and it starts right up. When it’s on half and won’t start, it still fires with starting fluid. I suspect there’s an air leak in some component in the tank.

Thanks for any thoughts.


#2

The next step will be to remove the fuel tank and inspect the fuel gauge sender/fuel pickup tube. I’m sure that’s where you’ll find your trouble.


#3

Does it have dual tanks?


#4

Yup… @asemaster stole the words right out of my mouth… Thats where I’d be looking

Either you are getting the wrong tank level readout…or you have an issue with the fuel pump and all its associated pieces.

@Barkydog brings up the second thought I had about dual tanks…whole other animal… Still not hard to repair really.

Blackbird


#5

I had the exact same problem with my 2005 Dakota. I finally removed my gas cap when the problem reared it’s ugly head and it fixed the problem. It always occurred at about the 1/2 tank level. A new gas cap was all that was needed.


#6

It sounds to me like the tank cannot breath in and is forming a vacuum as the gas is pumped out.
I’m unfamiliar with how the systems were set up in '83 pickups, but I’m going to guess that charcoal canisters were in use then and the tanks breathed in through them. Your charcoal bed may be saturated, perhaps from the previous owner “topping off” the tank. That would prevent passage of air into the tank, acting as a blockage.

You may want to look for a schematic of the truck’s evaporative emissions system. Perhaps the dealer’s parts guy can help with this.


#7

If it is a faulty sender unit, the OP could verify this by checking the mileage between fill-ups. If the mileage is about equal to half a tank, then the sender unit is more likely the problem.

The fuel gauge in our 2003 Silhouette reads either full or empty, and she won’t let me fix it (or have it fixed). She says it will cost too much. She uses the trip odometer to determine when she needs gas.


#8

Yes certainly try the gas cap removal trick to help see what you might be dealing with… I do this so often I forget I need to actually say it out loud or type it… lol


#9

Next time it happens, remove the fuel filler cap and see if that cures it…If it does, replace the cap or investigate the tank venting system as others have suggested. If removing the cap does not cure it, then your idea " I suspect there’s an air leak in some component in the tank." is sound and you will need to follow that up. Also, the entire fuel line from the tank to the fuel pump will need to be carefully inspected. Pay particular attention to any flex lines and rubber hoses in the system…In 1983, tampering with emissions control systems on trucks was a regular pastime. If done by non-mechanics, the cut and plug method, all kinds of problems can result.


#10

Hey everyone, thanks for the prompt feedback! @Barkydog no, it carries a single tank.

I did remove the gas cap and didn’t notice a pressure difference…still didn’t start after equalizing pressure, but then I didn’t leave the cap off, so I’ll try that method.

@“the same mountainbike” good idea with acquiring a schematic. I’ve been looking for one, but contacting a dealer/vendor might be the ticket.

I too fear it’s the sending unit, but wanted to mine for other thoughts before dropping the tank. Investigating other fuel system components first always helps.


#11

Dont be too shocked or resistant to suspecting the fuel pump assy… They fail all the time and no manufacturer is immune to this…it can happen to any vehicle.

Your unit is an all in one type of deal…which is how almost every mfg does it. It will be a big cylindrical assy made of plastic with the fuel pump motor…its pickup and screen as well as the tank float and fuel gauge sending unit…all in one shot… When you pull yours you might notice the problem…you might not. But have a new pump assy with you when you go thru all that trouble.

Order it off the internet…you will save a ton of money as opposed to buying local. At least that is what I try to do

Blackbird


#12

The '83 had a carburetor I believe.

It is likely that the problem is in the tank and removing it is a real pain working on a creeper.


#13

The OP stated the fuel pump has been replaced . If the exact same problem presents itself both before & after the fuel pump replacement I’d tend to think it’s something else . Usually the entire fuel pump & pick up tube , etc . are replaced as an assembly but I suppose it’s possible to replace only the pump & reuse the rest of the assembly .
If the complete assembly was replaced & the exact same problem persists that would be quite a coincidence .


#14

If the OP’s truck has a carburetor, and that appears to be the case, the fuel pump is mechanical.


#15

Correct, @“Rod Knox” the fuel pump is mechanical and next to the engine, not in the tank. Driver side mounted 19gal tank. It appears there’s one fuel line and one electrical line into the cap.

http://www.oreillyauto.com/site/c/detail/GT00/FG74A/01997.oap?year=1983&make=Ford&model=F-250&vi=1123704&ck=Search_01997_1123704_2751&pt=01997&ppt=C0025


#16

1983 F-250 300 cu. in. straight six…Fuel pump is mounted on the engine, feeds a carburetor…

The fuel pickup inside the tank is a fiberglass sock which acts as the primary fuel filter and they can indeed get plugged up…


#17

Measuring the fuel pressure and fuel delivery rate at idle might be worthwhile. Those are both fairly easy for a shop to test. They hook up a special in-line fixture with a fuel pressure gauge and some valves and a restrictor and can then measure the pressure and flow at idle. If there’s an accessible replaceable fuel filter, replacing that is probably where I’d start if I had this problem on my truck, before proceeding to the above tests.


#18

Two things maybe ?
The weak mechanical fuel pump spoken of. ( the gravity of a full tank pushes enough to help the weak pump )
or
a rusted pick up tube. little tiny holes in the rusted area ( caused by sitting parked for so long on a half tank ) allow it to suck air at that point.


#19

I finally got around to taking the truck to a mechanic…he disconnected the gas tank and ran a separate line to an external fuel tank and found the truck started and ran perfectly. So as many suggested, he ended up replacing the sending unit in the tank as well as the fuel lines. The truck now runs stronger than ever! Thanks everyone!


#20

Congratulations. Now we must award the winner and it seems that @asemaster has again taken First Prize… And the prize is in the mail @asemaster. Trust me.