When I turn key to start position, I have power on pump side of relay but when in run position pump side of relay is dead .if I hold key on and keep cranking engine power stays on pump side of relay ,as soon as you let go of key to run pump side dead . If I turn key to run without trying to start I have 5 to 7 second initial burst for fuel injection , then pump side dead. Can anyone help me , I am to the point of total frustration

Check the ignition switch for wear, pitting, or melting. My bet is that the ignition switch is bad. Not too difficult to replace.

The ecm won't turn on the pump relay when key is on but the engine is not cranking or running. It will power up for a few seconds when first turned to run position but if ecm does not get an rpm signal it will open relay. Check for power AT the fuel pump. Should be a gray wire. Don't over look the ground. Black wire bolted right to the frame. If power and ground are good at the connector the problem is either in the sending unit or the pump is shot. Gm never did make a very reliable fuel pump especially in a blazer. If it is the pump make sure you also replace the fuel filter or you will be changing the pump again very soon!