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You have a '97 M3 90K The fuel gauge is intermit registerng empty or full when actually half full and you hoped it would be a simple sensor replacemnt instead of entire instrum clustr for big bucks?

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August 05, 2006 8:23AM

Check the fuel sending unit first. It mounts in-tank and tells the gauge what to read. I have experienced "sticking" of one of the sending units in my 1997 M3. There are two, one on each half of the tank, apparently to increase accuracy of the fuel gauge during hard driving, or perhaps just to improve over the readings given by a single sender. I had luck by adding some fuel system cleaner, and allowing the tank to fully empty a few times, then filling up, in order to push the float to its extreme positions. The float, in case I am being too detailed, rises and falls with the fuel level in the tank, and is connected to a device which offers different levels of electrical resistance...which the gauge responds to in order to indicate the fuel level. Interestingly enough, my M3 was at just about the same mileage (95K or so) when it began to do this. Since then, I have logged an additional 30K trouble-free miles. It seems that just one of the senders sticks, causing erroneous readings on the fuel gauge. Mine refused to indicate less than half a tank of fuel. This would seem to indicate that one of my senders was sticking at the full level. The instrument clusters are 100% elecronic, and I have found them to be very reliable in the BMWs I have worked on. I have yet to replace one, although this of course does not mean that yours is not faulty, I would be least suspicious of the cluster, and look for other causes. Of course, this is an M3, and if you have a faulty sender, it will cost more than you think! Good luck, and don't hesitate to get the Bentley guide for your vehicle. You will see it on the mechanics' bookshelf at most BMW dealers...one indication of how good these aftermarket manuals are for these cars. I rely on mine for everything, especially since you cannot get factory manuals for these cars unless you are a trained BMW employee, and even then they give it to you class by class...