1981 F250 Sporadic Engine Stalls
 

First welcome to FTE.
You did not post what size motor as that may lead us to something else than what I listed below.

That is a sure sign the IGN box on the inside of the fender well is going bad.
It heats up and stops working and motor shuts off.
Motor off it cools down and will start working again.

This can do this for years if you can stand it that long or stop tomorrow and not work again.
If you find that it does the same thing you now have a spare for when it does goes bad.
Post back if it works or not and if not we can dig deeper.
Dave ----

Simply take the air cleaner off, look down inside the carb and push the throttle wide open. If you see two streams of gas squirt into the engine, you have fuel, and you can surmise you have a spark problem. Harbor Freight also sells a cheap spark tester.

Yep easy to do wile waiting for the tow.

How much fuel is the gauge showing?
I would also replace ALL the rubber fuel lines.
Should have a short piece at each tank to metal lines, more short pieces at the duel tank switching valve, short piece from the metal line to the pump and may have some between pump & carb.
Todays fuel eats the older rubber hose from the inside out even if it looks good.
Dave ----

Well to test the pump a long rubber hose into a gas can and see if it pumps.
I think the duel tank valve if it fails will only pull fuel from 1 tank not the other. Could always bypass the valve with rubber hose to check.
On the later years I think it can fail and not pump from either tank.

IIRC the gauge goes thru the tank switch on the dash. Have you tried to flip the switch back & forth a few times? The contacts could be dirty inside the switch.
To check the wiring & switch, ground the wire at the tank senders, turn the key on and the gauge should move to full if everything is good from tank to gauge.
If it does not let us know and we can dig deeper on it.
Dave ----

Thank you for the tips, I will do all of those tests. Getting a good diagnosis is a lot cheaper and probably more reliable in the long run than just throwing parts at it. Do you know by any chance ford used mechanical or electrical fuel pumps in 81? I can’t seem to find a decisive answer on that.

I am pretty sure the factory pump is a mechanical bolted to the left front side of the timing cover.
It is easy to find, start at the carb and follow the fuel line back to the tanks.
Some one may have installed a fuel filter between carb & pump and think the carb may have a filter screwed into it but not seeing it I cant say for sure, my 300 six it is screwed in.
If you follow the lines back from the pump on the inside frame rail under the cab you should come to the duel tank switch valve.
Has 3 hoses - 2 in 1 from each tank and 1 out let, should also have a think 2 wire plug.
Going back from there should be the tanks.

Now a PO could have added a filter anywhere in the system or an electric fuel pump, why who knows?
Dave ----

you could also have an ignition coil breaking down when warmer, mimicking fuel delivery issues, my 390 Galaxie did that and had me chasing carb issues quite awhile.

81 f 250 351 ... sporadic stall
 

I have a 81 250 with dual and I had the same problem.there are two low pressure pumps one in each tank and 1 high pressure on frame rail under drivers door and 1 mechanical pump on the engine my problem was one on the block sporadic pressure replaced it and it fixed my problem

10-11 years ago I had the same problem......the truck would start & run fine but would cut out as if the key was turned off, when left idling.

Over a period of months it slowly became worse, to the point that if you pulled up at lights it was almost guaranteed to cut out............& for some reason, always at an idle (only once ever while at driving speed).

Eventually I found it was a bad connection at the distributor loom plug. I cut the plug out & soldered the wires - it never recurred.

But if you have a fuel problem, the cutting out would typically not be instant - as it is with ignition.