anyone knows how can i fix that?

OK old post but I just fixed the same problem. My pump was pumping very little air and no pressure. Like in this old post the air was escaping trough deflate end. I took the whole thing apart. There is a smaller tube inside the pump shaft. When you reassemble make sure that that piece is centered thus it possible to screw the handle and the piston all the way. Otherwise there is a leak and no pressure.