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Big engine needs a good strong drive belt. Belts stretch after time and just need replacing. I would start there first. Next if you notice any sputtering when it's about to stall then it may be a bad or clogged fuel filter.
It may be gas or ignition related. Try to determine which, when it stalls and won't start. With key on, you should hear the fuel pump turn on for about 2 seconds to pressurize the lines and fuel rail on the engine. If you don't hear the pump, and have no pressure in the fuel rail with key on, it is probably a bad pump.
If the pump is working, check for a strong blue spark on a spark plug wire after it stalls. If no spark on any of the plug wires, suspect the crankshaft position sensor or the ignition control module. Either one can cause those symptoms- failing after it gets warm or hot.
Maybe the engine did run out of gas; if the pump quit working, that is it. Do you hear the pump in the tank turn on for 2 seconds, when turning key to on, not start? It should turn on with key on, to pressurize the fuel system. If you don't hear it, and you don't have gas up to the engine, the pump has failed or the pump circuit needs checked.
Sudden stalls while driving are usually gas or ignition related. And so we say: check for gas, check for spark. If you have no spark on a spark plug wire when cranking the engine over-the ignition system has a fault- will need electrical testing to diagnose it.
Do you know how to check for spark? You will probably need a helper to crank the engine over while you or someone watches for a strong blue spark. If you have it, ignition system is working, check fuel pressure and check injector circuit.
Easy way to check for spark without getting shocked: buy a cheap spark tester from parts store. Plug it into the end of a spark plug wire, and clip the ground clip of tester to a metal piece of engine. Now you will not have to hold the wire close to a ground- don't touch the wire at all when cranking engine: just watch for a blue, snapping spark.
Interesting. You may need a wiring diagram for the engine. Unplugging the regulator turns off the alternator which should not affect the ignition system. Unless it is over charging somehow. Or the alternator load on the engine is causing a missfire to be worse. Its possible you have a ground problem somewhere too.
It sounds like your fuel pump is overheating. Once it gets too hot the bearings swell and the pump locks up. When it cools, they contract and the pump works again. It is also possible the fuel pump relay is having a thermal failure. You can determine this by hooking a voltmeter into the fuel pump supply wire and keep it where you can see it while it is running. If the voltage goes down and then the truck stalls, it would be the relay, if the voltage goes down after the truck stalls, it would be the fuel pump. Since the pump is only running when the engine is running, once the engine dies it'll turn off the fuel pump so it is important to pay attention to what happens first.
Check if fuel or spark problem,..all engines need both to run...use starting fluid in air intake ,..if it runs very shortly-fuel pmp?,,ck for spark at spark plug,work your way back..also ck timing belt-intact? Kev-MN
On older, carbureted engines, cold stalling (and hard starting) is most
often due to an automatic choke that is sticking, misadjusted or
broken. Cleaning the choke mechanism with aerosol carburetor cleaner
may free up the choke allowing it to work properly again. If the choke
housing as an electrical heating element, the element may not be
receiving voltage when the key is on, or the element may have burned
out (check resistance with an ohmmeter).
Other causes of stalling with a carburetor include an idle speed
adjustment screw that is set too low (turn screw to increase idle speed
rpm). The engine may stall if the idle fuel mixture screw(s) are not
adjusted correctly or the idle mixture port(s) are dirty or clogged
with fuel varnish deposits (clean the carburetor and readjust the idle
mixture screws for smoothest idle). Stalling can also occur is there
are vacuum leaks in the carburetor, under the carburetor (bad base
gasket), or any vacuum hose connections to the carburetor or intake