My 05 f-150 Supercrew 5.4l, will start for a second and then die. I can sometimes feather it and rev it up, but it dies as soon as you let off.

I changed the fuel filter and while we had the lines off we turned the key on and it pumped fuel but only for a few seconds. Shouldn't the pump run constantly with an open line?

Any help would be greatly appretiated!

 

The initial surge of fuel is the pump attempting to presurize the fuel lines to keep the injectors primed. Once the motor is running it will pump to maintain the required fuel pressure. You really don't want the fuel pump to keep running with an open line.