Fuel supply issues

[bamagene44]

I just bought 1999 S80, Runs great until fuel gauge show 1/4 tank prox, then it acts as though it is out of fuel. Power lessens and will finally go dead. When you restart it will crank and run but will then behave as before util you raise fuel level. This has occurred fro 30-100 miles remaining. Car had been setting for a while so on initial fueling and start-up I used Seafoam. I also thought it might be water in fuel tank and ran fuel level down and used Heet, with no change in behavior.