Can you disconnect the fuel line from the pump to the turbine, put the line in a ground tank and run the pump in test functions
my guess is something in the fuel has tightened the gears, start at the 0.5 and go to 4v, leave it for 10secs, go down to 0.2v ( where it should still pump), back up to 4v. Do that a couple of times and try it again

Dave