1989 Ford F-350 won't start after it is warm

When this problem usually happens it is a failling injector pump. So when the parts get hot they have alot more clearance in them as to when cold. The injector pump had such tight tolerances that any wear and they would do stuff like this. The reason that they wear out is from when they rduce the sulpher content in the diesel at the gas stations. The sulpher is the lubricate that comes with the diesel. After you get this problem fixed you will have to start running a addative that bumps up the lubricant value. Howes fuel treat is the best one that I have seen and used on the market.