Why does it sometimes start and sometimes not?

Sometimes it starts and runs and sometimes it will not start (starter is good)
turn the key and engine cranks but no start remove air cleaner and squirt
start fluid into cleaner and crank engine, car starts and runs until start fluid is
gone after engine quits I crank the eng and it starts and runs revup no miss
turn off and it might start and it might not. Anti theft is not the problem and I
have no codes set, replaced the following Crank pos senser, Cam sensor
and fuel Pressure regulator. also fuel pump and Filter. Why does it turnover
and is firing injectors but not getting fuel but spray either into intake and it
fires and runs and sometimes until I turn off key, also engine will run with the
cam sensor out of engine and engine will run. any good ideas???