Sometimes won't start
 

It cranks but won't fire. At first I just thought it was the aftermarket key but it happened once today with the factory key. It has happened about 4 times in the last two weeks and eventually turns over after a few tries.

2004 350Z all stock ignition.

i had the same problem see if you can here if the fuel pump turn on when you cycle the key if not check the relay and the fuse for the fuel pump that what the problem was on mine they were lose for some reason hope this helps sounds just like what mine was doing