Electrical problem
2002 Other Oldsmobile Models 4 cyl Front Wheel Drive Automatic 150000 miles

The fuel pointer indicator on the dashboard is jumping back and for a while and later during the driving time shown a more gasoline in the tank than I have before refilling.
Another time after refilling of 20 liters of gasoline (app. 5. 3 galons) to the tank and driving a while the indicator showed me that I have almost empty tank.
What is wrong and how can I repair by my selves or I have to go to the electrician or dealer station.
Thanks for your respond.