I have a vent problem with he fuel system. I have changed the vent valve. on 2001 Chevrolet Blazer

The truck takes fuel at a trickle, so i unhooked the lines from the charcoal filter box.
pumped fuel went in fine.
hooked up the top line back to filter box
pumped fuel, went in fine
hooked up the bottom line fuel would not go in.
went home unhooked solenoid and blew through the line nothing in it.
so i checked the connection 6 volts with the key off, turned the key forward 11.8 volts (same as the battery)
Replaced solenoid with ACDELCO, still have the same problem.

Asked by for the 2001 Chevrolet Blazer