My 69 GS 350 Fuel Gauge Stays past f when running.When i shut off it goes down to what is probably a true reading,but when i start it again it goes past the f mark and stays.Thanks for any tips guys.Thanks John o No:
Gee, wish mine would do that - but no matter what I do, it keeps running out of gas. Seriously, though, I'd check the ground as Tim said. Also, if you can get behind the gauge without much trouble, check the pins. The plug goes over pins that stick out of the gauge's circuit board. Beind old, they are easy to break. However, if you haven't done anything behind the dash lately, its not likely. I also wonder if the float could be stuck (though I seriously doubt it).
An easy test: Find the fuel gauge sender wire(brown) plug at the fuel tank and unplug it. Take a test light, with the clip hooked to ground, and touch it to the brown wire going to the gauge. The gauge should read either full or empty (can't remember which, but there will be no doubt if it is working correctly). Don't forget to turn the key on . When you unhook the test light you should be able to see the gauge go to the same place it would when the key is turned off. If it does all that, you can be pretty sure either the gas tank isn't grounded good or there is a problem with the sender. There is a ground wire going from the sender to the body, check that or put a jumper on it before you decide to drop the tank. HTH
If the brown sending unit wire is disconnected (infinite resistance), the gauge should peg at full, and if it's connected and the gauge pegs out at empty, you've got a dead short somewhere (zero resistance).
If I'm not mistaken, the factory fuel sending unit on a '69 Buick (actually most '65 to '97 GM vehicles) reads 0 Ohms Empty (dead short with no resistance) to 90 Ohms Full. The other posts suggestions will certainly tell you if the gauge is properly connected to the sending unit, and whether it is functioning at all. They will not however tell you if the sending unit is still properly calibrated. Here's a trick: Once you get the other issues worked out, take a voltmeter with a resistance measurement function and check the resistance between the brown wire, and the PROPERLY GROUNDED fuel tank (Like D-Con said, no ground= no gauge)when the tank is FULL. It should read somewhere close to 90 Ohms. Anything way above or below that, and your gauge will never read right. Then, drive the car as you normally would, and try to get the gas level as low as you can (without stranding yourself on the side of the road somewhere!) and perform the same measurement again. It should read near zero. You mentioned that when you start the car, the gauge pegs PAST full and stays there. That indicates an open circuit (with infinite resisitance), and the gauge is trying to show you that "increased resistance" it is seeing (more than 90 ohms). Assuming the tank/sender are properly grounded, it sounds to me like the sending unit itself is bad. There is essentially a potentiometer (or variable resistor) coil that the float moves a contact across in the tank. This change in resistance is how the gauge measures your fuel level. Over time, sludge and contaminents can get into the windings of this coil and throw off the resistance, or create an open circuit (Which would peg your gauge past full on start-up). Hope this helps....
Just fixed mine about a month ago and it was doing the same thing.Sending unit in yank was bad Good luck ED
