1994,My Blazer will crank over but not start by itself. It needs starting fluid to start.

My Blazer will crank over but not start by itself. It needs starting fluid to start. I have replaced the fuel pump, filter, the whole spider injection system and it still will not start. My pressure is where it is supposed to be and it holds the pressure as well. I spray starting fluid in it and it will run at idle forever. Once I mess with the throttle it runs really rough and usually sputters out and dies. Once in a while it will run even when I open the throttle up but acts like its not getting enough fuel or the correct timing of everything because It'll start back firing and wanting t