jumped timing

i just wanted to know if my 2000 crown vic is jumping time and what that really is... when i put my key in my car and turn the key in the car starts and sometimes it doesnt but when it does start it just kills out, my engine is turning over, ive already had someone drop the tank empty it clean it out clean all injectors change the fuel pump all because it sounded like it wasnt geting gas to the engine all that didnt do anything, they said my car is running on 4 cylinders instead of eight though, i really dont know what to do ohh and i aslso bought the coumpter piece to see if that was the problem that was 250 dollers wasted, please help!!! and its not getting commpression