I have a 1991 D250 that would start and run but after awhile it would die just like I turned the key off. If I wait a little bit it would start back up. Some times it would run for 30 seconds and other times it would run for 30 minutes or longer. Now it won't run at all it will turn over just fine but won't run. It is getting fuel and no spark. I was told that the on board computer controlled the spark. Is this true? or is there a pickup in the distributor that might have gone bad? or is there a ignition module that could have went bad. Thanks for any and all help.

 

Had about the same happen in my '89... it was the pick-up coil ("Hall Effect switch") inside the distributor below the rotor. Replaced it and the problem went away. Best I remember it's held in with two phillips head screws. This is only assuming, however, if you're motor is a TBI motor, which it should be in a '91.

 

My 86 died while I was cruising down the freeway, no spark, cut out a few times then dead. It was the ECM on the firewall. Do you know anyone with a similar truck that you can borrow parts from to test? Otherwise it may be time to start buying stuff.