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If you do blow into the line as mustangII460 advised, you should get some slight resistance and detect some bubbling inside the tank. If not, then the pick up (the tube with the sock on it) is above the gas in the tank and is probably installed incorrectly. When the unit is installed, the pick up tube should be angled down towards the bottom of the tank. It also is possible that who ever sold you the sending unit could have given you the wrong one. That happens frequently in the parts business.

Rev