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I use my 85 F250 7.5L 4WD pickupo to plow snow and it ran with no problems.
It sat for a week and went to start it. It fired right off and ran for about 30 seconds at high idle and then died. It was like you turned the key off. Tried to start it and it cranked but no start.
Checked and it has spark. I checked the fuel and being alone attached a plastic hose to the fuel line at the carb. Fuel came up slowly in the tube while cranking and I quit because I didn't want fuel all over the engine.
Checked the inertia fuel cutoff and it is not tripped. The last time it quit like this was on the road and it was the distributor pickup coil.
I assume that it is electrical as it never coughed or sputtered as though out of fuel but died just like turning the key off.
I checked the fuel and being alone attached a plastic hose to the fuel line at the carb. Fuel came up slowly in the tube while cranking and I quit...
This is what you need to investigate, at least some more. It's spec'd to deliver X pints in Y seconds... place that end into a bucket and see how much it will deliver in 10 seconds, 30 seconds of cranking.
If you have the electric pumps, and there is something wrong with the fuel pump relay, the oil pressure switch that runs the relay, or the wiring/power to this system, it can keep it from running. The pumps get power from a wire over at the solenoid only when cranking. Once it starts running the pumps get power from the relay. So if you get it started or get fuel while cranking, but then it quits again, that's a sign.
The fuel pump "bypass" wire is connected to the small "I" terminal of your starter solenoid and this wire supplies power to the fuel pumps ONLY while cranking the starter. It is called the bypass wire because it bypasses the inertia switch, fuel pump relay, and oil pressure switch safety features.
It also bypasses the resistor wire and feeds a full 12 volts to the pumps which the fuel pumps are not designed for long term so you don't want to run the pumps on the bypass for very long.
Now with that said, you can run a jumper wire from the battery to the I terminal on the starter solenoid (be careful not to jump to the S terminal. That will trigger the starter which could be very dangerous, perhaps fatal, if the truck is in gear) to see if the truck will start and run. If it runs you've at least narrowed the problem down to fuel delivery and likely the main fuel pump power supply system.
Note: For simplicity this diagram omits the dual tank fuel selector.
I assume that it is electrical as it never coughed or sputtered as though out of fuel but died just like turning the key off.
A fuel or ignition problem? This would be a perfect example to try a burst of starting fluid for troubleshooting. Even though you have spark, maybe it's not strong enough to fire under the load of compression, but will look okay when tested in ambient air. Others have suggested a fuel problem. A two second burst of starting fluid will help isolate the problem.
If the engine fires right up on starting fluid, then you know the ignition system is good. If it stalls again as soon as the starting fluid is consumed, then you know you've got a fuel delivery problem. If the engine doesn't fire at all, then you know one of two things: Either you're not getting a proper spark (weak, nonexistent, or wrong time), or the plugs are flooded with fuel and can't fire. In that case, pull and inspect them for wetness to be sure before condemning the ignition system.
One warning I must include: Starting fluid is great for troubleshooting, but if you don't get any attempt to fire, do NOT keep using more. A single 2 or 3 second burst will tell you everything you need to know. Don't keep spraying and trying, as you could get a serious backfire or worse. Giving away my age here, but it's like Bryl-Cream: A little dab will do ya...
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