Quote:
Originally Posted by jackbauer
Little update on the bmw fuel gauge. I had some play time today so i hooked up a 500r pot and made some measurements. At 500r the wiper of the pot read 3.75v and the gauge read just over full. Reduced the pot to 3v then 2.5v. Gauge stayed the same. Recycled the ignition switch and at 2.5v gauge read just over half full. Reduved to 1v. Still no movement then recycled ignition and gauge reads about 1/8th.
So it looks like i can "fill" the tank as quickly as i like but it won't "empty" very fast. So it looks as if the stock gauge is useless for soc as its the opposite for an ev. Fast drain and slow fill. I'll be getting rid of the bmv600hs battery monitor soon now that the lcd module can measure charge and will just fit a normal resistive fuel gauge in the pod.
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That's the expected behavior for software-driven BMW fuel gauges.
The instrument cluster computer has special code to make a better guess at the actual fuel level. It appears to have been added after BMW had a problem with the senders getting a dead spot (from corrosion?) in the presence of alcohol-containing fuels if you overfilled the tank. The software "knows" that you can't empty the tank instantly, and ignores any quick drop in the sensor reading. When the firmware update was introduced people complained that the gauge remained on 'F' until four gallons or so were used -- a side effect of the software work-around for the hardware problem.