I have a 89 150 custom 4.9L duel tanks.It has a problem with the front fuel tank.I have searched fuel problems not found what I need.I'll throw this out and see if any one has had this problem.My front tank does not work at startup or on surface streets.I can hear the front pump humming loud.When I'm on the freeway and switch tanks the front tank will work untill I get off the highway and slow down.I appreciate any help.Well gotta go to work.

 

re-place the pump..

 

You are hearing the frame pump. It gets loud when the tank pump doesn't pump fuel to it.

 

Thanks Sean.That helped me understand what's going on.Thanks techrep for your response.