2004 hyundai sonata

I would verify fuel pressure and delivery volume with half a tank and then below 1/4, I suspect the gauge reads inaccurate. Hyundai as a car manufacturer put a lot of free technical information and workshop manuals on line for Hyundai owners. Check out www.hmaservice.com lots of great information. There is a company that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subrcription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have ,much better than generic workshop manuals from parts stores, much cheaper than the factory manual try http://www.eautorepair.net/Marketing/Default.asp?VID=125669 and get an online repair manual subscription if you decide to replace the fuel pump or gauge yourself.