2004 f150 5.4, been having a problem in the morning not turning over, changed the fpdm ,Still same issue,I have to use starter fluid every morning to start it and it runs fine all day? Last night I took the gas cap off and this morning started right up?? What could this be?

 

Does the fuel pump itself engage when you have the key in the ignition and turn it over? Everything needs spark and fuel so start with the basics.

 

The fuel pump is fine, the last 2 nights I left the gas cap open it starts fine,is it the gas cap? Pressure build up? The truck runs perfect ?

 

If I had a spark issue the starter fluid will not work and if it was the fuel pump the truck would only run on starter fluid.