I have a 2004 350, when I fill up with gas my gauge doesn't register that I'm full. It registers that I'm 3/4ths full. While I'm driving it fluctuates quite a bit going up and down so I never really know how much fuel I have left. Same with the DTE meter. When I'm full it says I have roughly 280 miles dte but when I'm driving along I check it and sometimes it goes above 300 then dips back down below 250. I'm not sure what the issue could be. Any advice would be awesome.

 

Sounds like your in-tank fuel level sensor has seen better days. Here's the OE part:

https://www.z1motorsports.com/electrical-units/nissan/oem-350z-fuel-level-sensor-p-12533.html?osCsid=r21df52hmmnqbvg72qj79f9o40


Disclaimer: There is a possibility that it could also be a wiring issue or oxidized connecter. Be sure to troubleshoot before you buy a part you don't need.

 

 

And remember, there are two fuel level sensors, one on each side of the fuel tank.

 

Yes, Karlt's right. Check both tanks. Troubleshooting is outlined in the FSM (http://nicoclub.com/archives/nissan-...e-manuals.html)

Also, there's a sticky on this topic already:

https://my350z.com/forum/maintenance...d-to-fill.html

For what it's worth, unless you're comfortable digging into your fuel tanks and unless you have the proper diagnostic equipment and can follow safety protocols, leave this to the professionals.

 

Have you recently serviced the fuel pumps? There's a chance it might be the hose inside got caught up on the floater of the fuel sensor.