Cadillac Repair: gas tank sensor, variable resistor, gage wire

Question
why does my gas tank always read full. What can I do to fix it.91 cadillac deville

Answer
Hi Carlton, Your problem might be inside the gas tank like the baffle is loose and holding the float up or somehow the float disconnected from the arm in the full position. One test you can do is safely raise the rear of the car on ramps or jackstands and slide underneith and disconnect the 8 wire connector for the sender on the RH rear side of the tank. Turn the key on and if the gage flashes E then your problem is inside the tank. The only other possability is if the gage wire is shorted to battery voltage somewhere then it will read full all the time. If this happened after a repair was done then retrace the repair and you might find the problem. Otherwise it sounds like the gas tank will need to come out and the sender checked. But before you do get a variable resistor from radio shack...like a volumne control ...that can change its resistance from 0 to aprox 90 ohms or just buy a couple resistors and with that sender connector unplugged and the key on jumper the resistor between terminal F(purple) and C(pink/black) on the gage side and if the gage shows readings somewhere between empty and full then you know your problem is inside the tank with the sended or the wireing. You will need to get terminals that are the correct size to fit the other terminal so you don't spread them and create more problems. If need be flatten the end of the resistor with a hammer so it is the same thicknes before pushing it in or buy a female terminals so it can slide on the spade terminal.
Hope that makes sense. If not then you will need to take the car into the shop for diagnosis and repair. With my past experriance if the tank does need to be removed it might be best to take it in anyway because on an older car like yours the fuel lines and bolts can get pretty rusted up and you need the car up at lest 18" for tank removal. In addition if you have more than 3 gal. of gas in the tank you will need to be able to remove and store it safely otherwise because as soon as you remove the big hose on the tank gas will start comming out. Sucking on gas to remove it from a tank can do serious damage if tasted or swallowed so a syphon pump such as used with kerosene is a must and no pumps run with an electric drill eithor as the drill motor running can cause the fumes to ignite and then an explosion. Hope that helps. Bill