No start without return clamped
 

I have a 2000 zr2 Blazer. It sat for a couple years before I bought it from my wifes cousin. I replaced the fuel pump and pressure regulator, but it still will not start without clamping the return line shut. I was thinking it's probably the injectors, but I'd like a second opinion before I spend the money.
Withe the return line clamed it starts, runs good, and drives; I only moved it 20 feet to get it into my shop.