I've had this problem since I've basically owned the car which was since 2008.

When u fill the car up or when it approaches empty, it sometimes reads right and sometimes doesn't !

Example: when approaching empty it'll show it have 0 fuel and then maybe 15mins of driving correct itself or one day it'll work perfect.

What do u think it wrong and what parts should I replace?
I'm doing a turbo upgrade so when I do my fuel pump
I can deal with it

 

I have the same problem, but maybe not as severe. The fuel gauge tends to wander a bit, so I basically go by how many miles I've driven on that tank of gas and try to fill up early instead of risking an empty tank. This is probably something to do with the sending unit in the gas tank. If you are going to put in a new fuel pump, it probably couldn't hurt to order a new OEM sending unit and make sure the arm is sitting correctly.