HELP - 1991 Jeep Cherokee Laredo 4 X 4 Engine won't start

One easy test is when you have the no-start condition, try turning the key on and off a half dozen times without actually cranking the engine. This will help build up pressure to the fuel rail. If it now starts, it's probably the pressure regulator, weak pump, or a clogged filter. You can also put a gauge on the rail and check it that way, assuming you have the tools.