Truck will start up and idle great for a while then it just shuts off

Welcome to 2CarPros.

First, if you haven't already, pull diagnostic trouble codes that may help us narrow things down. Here is a link that shows how to do it on a GM OBD1 system. All you will need is a jumper wire or even a paper clip.

https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

Let me know if there are codes stored.

Also, keep in mind, the ECU monitors input from several different areas to determine spark timing. Here are a few of the things it uses.

The ignition system has a distributor module with four terminals for the EST system that are connected by the ECM.

To properly control ignition/combustion timing, the ECM needs to know the following:
^ Crankshaft position
^ Engine speed (rpm)
^ Engine load (manifold pressure or vacuum)
^ Atmospheric (barometric) pressure
^ Engine coolant temperature

I have seen the engine coolant temperature sensor cause the fuel mixture to be so far off that the engine will carry on and then stall. It's just food for thought at this time. Also, make sure the are no vacuum leaks that can cause issues as well.

Let me know what you find.

Joe

Thanks for the advice. Will be looking in to all that tomorrow. I will let you know what code or codes it pulls. And go from there. I'm at the end of my rope with it. But I refuse to give up on my old truck.

Welcome back:

Let me know what you find. And I have a 1978 C10 that I will never give up, so I understand. LOL

Take care,
Joe