My 2004 g35 will knot start with out a jump. I would stall out a lot so I talked to my friend he told I may have a bad fuel pump so I replaced it also new crank and cam sensors I also put on a electronic throttle body. Now I was told it needs and high pressure fuel pump.the crazy thing is after I get out of the shop the car runs better than ever please help me get her back on the road

 

Firstly keep an OBD2 scanner in the car so you can check for codes when it's malfunctioning.

Second buy the Z1 Motorsports VQ fuel pressure sandwich adaptor so you can actually test fuel pressure when it's malfunctioning.

Thirdly, did you use OEM or Hitachi for those cam/crank sensors? This car is notorious for not working with aftermarket. Hitachi was the OEM supplier.