Cranks but wont start 2002 ford xlt-150 supercrew 5.4 starts when primed then dies off.

There should be a check engine light on**yes/no? this is either the idle air control valve,throttle position sensor or a fuel pump driver module ,fuel pump,fuse,or relay,clogged fuel filter all are possibilities here//// to rule out fuel pump/driver module/filter/relay disconnect the fuel line at the fuel rail wrap a towel around the lines connector and have someone crank the engine for 2 seconds if fuel is present at pressure then that stuff is ok then move to the idle air control valve,throttle position sensor and check those fuses this is a fuel delivery or electrical problem be patient and right down what you have done to narrow down the possibilities you can test the electronics with a meter also check the connectors I'm not there obviously so all I can do is point you in the right direction so (1)fuses/relay check all(2) disconnect fuel line and crank the engine checking for fuel delivery at pressure(3)if check engine light is on and it should be get the codes read you can borrow a code reader from auto zone this will make life simpler and you will find out easier whats wrong or buy one from a auto parts or sears,walmart but don't buy a cheap one if your going to spend the $ spend at least$200.00 and get something that will give you live data Innova, craftsman,etc.