gas gauge/gas-miles remaining anomaly

I have a 2002 330c. I had it tuned up just before I went on a trip from DC to Panama City Florida.
On the way back whilst driving on I95 I exited to get gas. My gas gauge needle was just above the empty line(the empty line was visible) and the computer said I had 29 miles of gas left. The low fuel light was on.
As I hit the top of the exit ramp the car started to sputter and I barely made it to the station before the car died because I was out of gas. The needle was still just above empty and the computer said 28 miles of gas was left. If I had waited one more exit I was screwed.
After I filled the tank the computer said I had 415 miles of gas left and I got back to DC without a problem. From then on I never let the car get much below a 1/4 tank.
Is this kind of inaccuracy to be expected? Could long drives where the vehicle speed is consistently 80mph cause this kind of problem? Could there be a sensor malfunction?
Thanks
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ted wrote:

Sounds like your sending unit is lying. Generally there is some error, but it is found on the other side of empty (on both). Since both the gas gauge and OBC rely on input from the gas tank sending unit to tell it how much fuel remains that would explain why both were a bit "optimistic". Know this now you could always just subtract ~30 miles from the OBC's estimate or have the sender replaced. But then you'd have to find out where empty is on that one too...
--
-Fred W

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The miles remaining is only an approximation based on the computer's knowledge of how much gasoline has been sent to the engine and the fuel level indicator's report of the gasoline remaining. The gas gauge and the fuel level indicator are not precision instruments. Nobody should wait until the low fuel light is on before stopping for gas. Jim
<DIV><FONT size=2>I have a 2002 330c. I had it tuned up just before I went on a trip from DC to Panama City Florida.</FONT></DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV> <DIV><FONT size=2>On the way back&nbsp; whilst driving&nbsp;on I95&nbsp;I exited to get gas.&nbsp;My gas gauge needle was just above the empty line(the empty line was visible) and the computer said I had 29 miles of gas left. The low fuel light was on.</FONT></DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV> <DIV><FONT size=2>As I hit the top of the exit ramp the car started to sputter and I barely made it to the station before the car died because I was out of gas. The needle was still just above empty and the computer said 28 miles of gas was left. </FONT><FONT size=2>If I had waited one more exit I was screwed.</FONT></DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV> <DIV>After I filled the tank the computer said I had 415 miles of gas left and I got back to DC without a problem. From then on I never let the car get much below a 1/4 tank. </DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV> <DIV> <DIV><FONT size=2>Is this kind of inaccuracy to be expected?</FONT></DIV>Could&nbsp;long drives where the vehicle speed is consistently 80mph cause this kind of problem?</DIV> <DIV>Could there be a sensor malfunction?</DIV> <DIV>&nbsp;</DIV> <DIV><FONT size=2>Thanks</FONT></DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV> <DIV><FONT size=2></FONT>&nbsp;</DIV></BLOCKQUOTE></BODY></HTML>
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As others have mentioned, this is most likely a sensor error. There are two fuel level sensors (at least in my E36 - think it is the same for you) in the tank - one for each side of the saddle bag. Both units are supposed to read 250 ohms when full, and about 10 ohms when empty. Problem is BMW is not very careful about calibrating them.
Since one or both of your sensors is reading high (saying more gas than actually there) you can calibrate the sensors, if you wish. Did this with mine, since I drive long stretches in CA and Nevada, and the last thing I want is to run out of gas in the middle of nowhere. Procedure is simple. Just place a 1/4 watt resistor in parallel with any sensor that's reading high. Compute the resistance so that you will bring the sensor unit to 250 ohms, or slightly less at a full tank. In my case it took 2000 ohms across the passenger side unit - driver's side unit was ok.
Now it's great. On a trip when gauge shows 1/2 tank, I'm down 8 gallons + - 1/4 gallon, or so. At only 1/4 tank, I'm down 12 gallons. So gauge is essentially right on the money using 16 gallons as a full tank - leaves me with the extra 0.4 gallons or so as a reserve. Now I just mentally compute mpg on the first 8 gallons of gas, and estimate when I'll need gas next without going below 14 gallons or so. Works like a charm.
Frank
ted wrote:

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