Chevrolet Repair: 95 Blazer Fuel pump power problems, haynes manual, fuel pumps

Question
I have put 12v directly to the pump and it will run and the truck starts. When testing the power at the tank with key on no power. when starting only 10.8 volts and up to 12.3 briefly as key is released. I have put in a new relay. I get 12v on the top two legs of the relay plug at all times, key off or on makes no difference.

I tried the test lead initially and the pump ran with 60psi and the truck would start. but that doesn't work now. Is there a fuse I have blown and I am not clear where the oil pressure sensor is, could that be the problem. I have a haynes manual but I can't seem to figure out what to check next.

Answer
You say that it will start when you jumped the test connector to 12v, correct? Then the circuit to the pump should be ok. With the key in run the pump will only run for a second or so just to prime the system.

Are you sure it's just not a weak pump. Relieve fuel pressure if any. From the lock position turn the key to run. Do you get any fuel pressure reading. You should get 58 to 64 psi and when the pump shuts off, the fuel pressure should hold, not bleed down. If you have any fuel pressure,even lower then the circuit to the pump is ok.

Fuel pumps & pulsators are known for going bad in these vehicles.

Get back to me with more info.