I have a 1995 blazer with the 4.3L V6. I have recently changed the spark plugs, wires, cap, and rotor. This made no difference. The vehicle doesn't start right away and shakes hard when accelerating. No engine light. Black soot on the end of the tailpipe and oil level rises and needs to be changed frequently. Help.

 

A fuel pressure test will verify that you have a fuel leak internal to the intake plenum which is common on the CPI motors. At the very least you could possibly get away with replacing the FPR (fuel pressure regulator) if that is where the leak is occurring.

The other possibility is that the 'nut kit' (internal fuel lines) is leaking. You won't know for sure what is at fault until you pull the upper plenum off. Once you have gotten it opened up, I would recommend replacing the FPR even if it isn't leaking from there.

 

Is the FPR on the spider injector assembly?

 

Yes.

The tech article on that topic should explain everything:
Fuel pressure regulator on Blazer 4.3L CPI W engine