Wrong reading on fuel gauge

Normally this problem is due to a bad sending unit. The sending unit is the actual device which transmits the level of fuel in the tank to your fuel gauge. The most common cause is a stuck float. The device works by means of a flotation device, often made of a petroleum resistant plastic encasing a foam or cork "float, " which is attached to a light weight metal arm. The arm moves as the float raises and lowers with the level of fuel. This arm connects to a switch which increases and decreases resistance in the circuit. If the arm is stuck or if the float is allowing fuel in it you will get an inaccurate reading. A "logged" float (one filled with fuel) usually reads below the level, whereas an arm which is sticking will read above the level. Now, if the gauge has been reading this way since the car was brand new, the other likely cause is that the needle may have been improperly placed on the gauge at the factory, or the windings in the gauge may be under or over wound causing the inaccurate reading. If you are mechanically inclined you may be able to replace the sending unit yourself. Keep in mind this can be a dangerous procedure for a first time mechanic as it may involve removing the fuel tank from the vehicle. Some vehicles offer access to the upper portion of the fuel tank via an opening located in the trunk under the trunk mat/carpet or under the back seat. If this is the case removal of the fuel tank is not normally necessary, but you will still be working with the fuel tank. If you are able to do this procedure in the vehicle, keep in mind you will first want to disconnect power to the fuel pump and sending unit. You can disconnect the negative battery cable, but I believe on an the kadette you will need to obtain a special cable from your local auto part supply to maintain power to the ECU or PCM to prevent damage to the computer or loss of programming. At the very least remove the fuel pump relay and disconnect any fuse/relay related to the dash gauges prior to beginning this operation. Also be sure to remove the fuse for any possible ignition source inside your vehicle, such as dome and courtesy lights. Keep cell phones away from the work area as well. If you use a "trouble light" be sure it is marked as safe for use near fuel fumes. Keep doors or windows of the vehicle open to allow vapors to escape so you don't suffer any ill effects and to further reduce ignition hazards. If you must remove the fuel tank, practice good safety. Do not be under the tank at any time. Be sure to remove it with very little fuel in it. Go slowly and be sure you don't break any wires or lines. It is a very involved process and may be best left to a certified mechanic or at least one who is very experienced. Keep me posted and let me know if this helps!