"1991 BMW 3-series: Fuel Tank Float Problems"

White 1991 BMW 3-series Front Left View

I have an 1991 BMW 3-series. The fuel gauge works in that when you turn the car on the needle go’s up to just under 1/4 of a tank, but no matter how much gas I put in there it wont go up and no matter how much I drive, it won’t go down. Is there some kind of float in the tank or something? If yes, how would you go about trying to fix that, short of going to a mechanic?

Answer: You may have a bad SI board but first lets do a little test. Take out the bottom of the back seat and on the passenger side there is a black circle cover remove that and look for 4 8mm nuts. thoes nuts hold in the sending unit. Just pull the wires and pull it straight out. Once you have it out you should be able to flip it over and over and hear a slight rattling if you do the float is free if not you may have to shake it or bang it around to free the thing. If you hear it moving around plug it in and turn on the car and flip it over and over and see if the gauge is going up and down. If so you have fixed it if not replace it. You can ground one of the wires (brown) and the gauge should go to full as you do. Its a good Idea to get a new rubber band seal when reinstalling. Old seals don’t like to reseal and you will smell gas after you fill the tank. Its uncommon for the sending unit to fail but it does happen.

If none of this works then you have a bad SI board. Programmed has new ones that work well. Repairing the old board is possible but I find they fail soon to just a few years down the road. The 300 buck price is worth it.