If the sender is like the EA's it will increase resistance the more petrol you have.
You may just have dirty connector terminals on your pump and wiring connectors, as it's very important they are clean and not corroded.
Fill your car up with petrol, and when you turn on the ignition, watch the fuel guage and see if it goes all the way to the top before dropping to the bottom showing empty. This is the guage overloading due to the resistance being so high from correded terminals. You can clean the terminals in metho and that should fix it for a short while, but the problem will probably come back until you replace the wiring connectors.