2005 Ford F-150 with 5.4 engine. sometimes turns over but won't start.I spray with starting fluid and it will start running.

Do you have spark and fuel pressure? Check the inertia switch? You might try a spray of starting fluid. If it tries to start you would know that the engine has spark, but the injectors could be working without fuel pressure and starting fluid would show you it is a fuel pressure problem if the engine fires with starting fluid.

is the engine light on or other warning lights glowing

if so there are fault codes in the ecu to be read

can be a fuse
or fuel delivery to the motor
or coil /spark problem

Turning over the engine, is not the same
thing as a no start condition

Won't turn over, means the starting system
is dead

Do you have the correct fuel pressure at the fuel rail
with a pressure gauge or on scan tool data, when the
key is turned on & also when running

About 42 lbs pressure

I would suspect you have issues other then fuel
& the spraying is just a coincidence

I think only scan tool or oscilloscope data on
several sensors, will be needed to see what's
missing on start up

How many miles on the car? Have you checked the fuel pressure when it doesn't want to start? Do that first and then move on from there. To quickly test fuel pressure with no special equip get a can of starting fluid from the auto parts store, when it fails to start spray the fluid into the air intake of the engine well it is cranking, if it fires up then the fuel pump is likely not running on for some reason. This can be electrical in nature or just a failed electric fuel pump

fuel pressure is to low by 10 or so pounds should be 45 with engine running 50-60 engine off key on reck pressure to be sure.

check fuel pressure, should be 40 psi.
try 2 things

spray starting fluid in air intake to see if it will stay running. It's fue then.

Try turning key to on nd wait 5 seconds for system to build pressure and pump to shut off. Turn key off, wait for relay clcik noise or 10 seconds. then turn key to ON again and wait 5 seconds to build pressure again. Then start engine. If it starts better, you have a bad check valve in the fuel pump or a bad pressure regulator on the fuel rail (unlikely).

report back

i would check the fuel filter if thats not it then it will most likely be the fuel pressure regulator make sure the vacuum line didnt fall off of it if that checks out then id say its your pump good luck i hope this helps

when it does this spray starting fluid into the air intake of the engine at the air cleaner and see if itr starts, if it does you have a sticking fuel pump..

Check for spark. Also listen for the fuel pump to kick on or spray starting fluid in the throttle body to see if it starts. If the fuel pump isn't kicking on then its your fuel pump and its located in the tank

Spray starting fluid near the carburator if equipped. It may be a leaking main gasket under the carb.If you spray and the engine turns off. It is a vacuum leak. meaning the main gasket under the carburator .