Fuel gauge
 

My fuel gauge shows a full tank at 3/4, a 3/4 at half, and anything less it just pegs 0. Yet, my low fuel light works...

Any ideas on fixing the gauge accuracy? I use this as a DD so it's kinda nice not to have to rely on setting the trip.

You must have an idea on what type of car you have and the series.
It would be nice if you could state that so people can help you.

Sorry, it's an 87 na.

So s4? Not 100% sure on those designations.

Sounds like it could be fuel level sender. This is judging on the vague information given. Is it modified? Does it have any alterations done to the fuel system? Make sure you clean your grounds and make sure you have good solid contacts on your connectors.

The fuel level sensor (for the gauge) is a potentiometer linked to a float in the tank. Worn or dirty contacts change the relationship between fuel level and voltage. Or, as in your case, there is a dead spot and below that level, there is no signal at all. You may be able to bring it back to life by removing the fuel pump assembly and cleaning the sending unit. More likely, you live with it or replace the sending unit.

The warning light is a separate float switch, which is why the light can work even when the lower half of the fuel gauge does not. Can also be the other way around.

Also in addition to RobbyWallys answer, in the FSM, you can diagnose whether the fuel sender unit is bad by taking the resistance on the contacts and making sure they have the necessary ohms it should have. If not then I recommend just replacing it.

removed the parts and cleaned them-- no change. Can you buy just the sending unit or is it a whole new assembly? I know just the pump runs about $150.

thanks for the help guys.