you probably need to replace the float or sending unit. which means taking the tank out.
It"s more than likely that your instrument cluster needs replacing. This happened to me, bought one at salvage yard for $55.00. If one component on dash stops working i.e-gas gauge temp. gauge speedometer, the whole cluster needs replaced.
It means the filter needs replacement
bad sending unit in tank, or short in wireing.
You have a grounded sending unit. If the gauge reads full all of the time then there is a bare wire or the sending unit itself has gone bad and grounded out. I also had the same problem after i swapped my fuel pump with one out of an older car that had been sitting for a couple of years. The float was either stuck or not working i just put the old one back in after i found out that it wasnt the problem with my car.
One reason could be the sending unit has failed.Since it is a part of the fuel pump assembly, inside the gas tank, repair/replace is not an easy job.See "Related Questions" below for more
probably no gas, if there is gas then your gauge in the tank is broken or frozen
Could be a bad fuse - fuse # 17 is a 15 amp fuse for the fuel gauge Could be a bad float on the fuel gauge sending unit inside the gas tank ( it's with your electric fuel pump ) If the float gets a pinhole or crack in it , the float fills with gas and sinks so the gas guage reads empty all the time Could be a wiring problem
bad ground or float stuck 2 possibilities i can think of
The fuel gauge on a 1985 Chevy Silverado will read full all the time if the sending unit is defective or the wire has come loose. When the tank is full, the sending unit normally shuts off which cause the gauge to read full.
Place the rain gauge in an open area (far from trees or buildings or anything that could interfere with rain falling on it. At regular intervals read the gauge record the amount with the date and time and empty the rain gauge.
The gas gauge sensor is most likely stuck. It is inside of the tank and over time it will get corroded.
take the gas tank down and replace the fuel sensor.
probably the sending unit. unfourtunatly the sending unit and fuel pump are made in one peice, so expect it to be expensive