In my 1991 Ford Ranger i had the same problem i just replaced the float system and this fixed the problem. Mine was on the inside or it wouldn't be able to detect the amount of gas left in the tank. You have to drop the gas tank. Make sure it isn't full when you do this or be care-full not to spill gas on you. It could be a little heavy also if it is full of Gas. Or it could be the in the gas gauge also. Before i replaced the float i checked the gauge first.