03 Duramax C4500 Starting Issue

[96chevy7.4L]

Hi guys. New to the diesel world. I bought a 2003  C4500 crew cab truck with a D-Max. I bought it cheap at the repo auction. Well it said unknown starting issue. I believe it to be a fuel pump as it spins over but don't crank. I hope its not the injector pump. How can I diagnose which fuel pump. As I don't want to replace both. I put a relay in it and it didn't cure it. I understand it has an electric pump in the tank and an injector pump. Any ideas.

[youcantkeepup!]

it prob needs injectors, try a new filter and prime it up that can get it to start sometimes with bad injectors

[96chevy7.4L]

the info I got said the injectors were replaced by chevrolet like 2 years ago. Do they go bad even after replacement. I took one end of the fuel filter in the engine bay off and no fuel passed thru. I replaced the fuel pump relay and still nothing. I have new filters on the way they should be in tomorrow. Any ideas in the meantime.