I filled my tank but the gauge didn’t go past 3/4
i saw that cleaning the se done in the sending unit and the level sensor could fix it,I tried it, but still didn’t go past 3/4
any ideas or what else it could be?

 

Did you clean/check both fuel level senders (driver's side & passenger side)?

Also, have you confirmed your tank is actually filling up all the way (Full capacity is 20 Gal, but I've never seen my tank fills exceed 18 Gal due to reserve)? There's a TSB about 350Z fuel tanks struggling to fill up the tanks with modern pumps when you get beyond the 1/2 mark. If you're getting between 15-18 Gal in the tank during a fill-up, then you should be hitting the full mark on the gauge.

As a last resort, you could use a multimeter to test the variable resistors for both fuel level senders. If they are not within spec, replace them, it's cheaper to replace the entire fuel pump assembly if the sender on that side of the tank fails. Resistance specs in FSM snapshot below.
Cheers!
-Icer

 

Thank you for the advice
i did clean the sensors in both sides and tested it with a multi meter,the sending unit had a range of 3-65 ohms and the level sensor read 3-42 ohms which might be it
and the last time I filled it up from empty I only got up to 17 gallons

P.S.it just randomly fixed itself I think,after I cleaned it I put gas in it but it still had the same issue but after the 3rd-ish time putting gas,it started working like normal

 

Hey smop,

Yep, it looks like your main sending unit is faulty. The "sub" sender appears to be within spec. If you got 17gal at fill-up, then you should be full.

Personally I would replace the entire pump assembly, which includes a new sender. But it looks like the prices have jumped recently. Note: There are differences for the Pump Assemblies depending on the engine you have (DE vs. Revup & HR).
Cheers!
-Icer