1990 Mazda B2200i Wont Run

Hello I have a 1990 Mazda B2200 Fuel Injected. The Car Wont Run? It will start up (for about 4 seconds) after sitting a little while then it will die and not start up anymore. we just replace the fuel filter and fuel pump. what else could it be? and how could it be tested? Thank you so much

Disconnect the fuel line from the rail and turn the key on?
That would determine whether you're getting fuel?

If so, then injectors may be clogged

May also be a clogged cat... did it get progressively worse?