fuel pump?, junk yard, local auto

Hello, i bought a used fuel pump from the junk yard, paid $45.00 for it, and i think its going bad, the car keeps dieing out starving for gas, and i hear a hissing sound from the tank.

The junk yard gave, 30 days to return it, and they want to test it out, when i do, they tested it out when i was there but just hooked it up to a battery to show me the motor works. I'm sure they are going to give me crap when i return it.

Is there a sure fire way to test a fuel pump, to make sure it works correct, without having to put it in the tank?

Should i even bother with a junk yard? Is there someplace i can buy a new one, or slightly used on cheap, and have it delivered, for a good price?

Answer
fuel pump for what kind of car? Seems to me that the junk yard gave you a pump that is still working but about to go out. When it hisses like that, that means there is corrosion in it. Try to run a Fuel system cleaner that you can buy at a local auto parts store. It might impove it. Follow up with me with your make and model.  
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