I’m trying to fiure out what is wrong with my son’s jeep. He has a 1993 Grand Jeep Cherokee, 4 cylinder and it goes through periods where it will start then die, start and die. It doesn’t seem to matter what the temperature is. It will start and run for a month or two, start acting up again.

Start with fuel diagnosis. Ensure that the fuel filter is newish. When the truck is stalling, spray starting fluid into the air intake. If the engine continues to run on starting fluid, you can be fairly certain that the problem is fuel supply.
The fuel supply problem could be from lack of fuel pressure, or lack of fuel injector action. Attach a fuel pressure gauge and monitor it during the stalling periods. You can check the signals to the fuel injectors with 'NOID Test Lamps.

I read in a book that it could be the timing chain???