PT pump

You need to put some photos up or maybe a small video if it will post.

If it were me, I would want to isolate where the problem is. So take off all of the external linkage so that you just have the shaft itself showing like you're going to take that pump off and take it to the pump shop.

Take your fingers and turn the shaft back and forth. It should be free and easy for you to turn by hand.

If it is hard to turn you have an internal problem within your pump probably rust or crap from your tanks.

If it is easy to turn your diagnosis is complete. The problem is not in the pump it is in your linkage.

Reconnect your linkage and make sure it is not against the pump as has been said, and trace your problem back. If it's not in the pump it's somewhere between the pump and the pedal.