Erratic fuel gauge.?

Question

1998 BMW R1100RT
With a full tank, sometimes the gauge shows full, sometimes it doesn't. Somewhere around 3/4 of a tank it drops to a zero reading.
The low fuel warning light dutifully comes on right around the last gallon of fuel... in other words I'm being a big baby about it but it would be nice if all the bells and whistles actually worked, ya know?
Anyway I put in some "fuel system cleaner" that was supposed to remove "sulphur compounds" that are known to cause this kind of problem - didn't help.
Ideas anyone?

This is the goop I tried. Didn't seem to hurt anything...
http://www.chevron.com/products/prodserv/fuels/additives/concentrate_plus.shtml

Answer 1

i own a repair shop,and i have seen the problem your having before ,its caused by a bad or loose ground wire in the rear of the vehicle there is a ground wire back there that comes off,and sometimes it breaks when it does the fuel gage tries to get a ground from somewhere else,and usually it can,and this causes the erratic movement in the gage its self,other wise a bad sending unit will do the very same thing on it,,i have seen them do this,and straiten out and never do it again,cars are like people they all act up once in a while,it has to be one one these things,id say you probably got a sending unit going bad on it,good luck,i hope this help,s.

Answer 2

First check that the float on the fuel level gauge isn't stuck. Remove it from the fuel tank and manually lift the float. Does it move freely? With it plugged in and you lift the float, does the gauge on the dash work properly. Next thing to try would be to replace the fuel level gauge in the fuel tank.

Answer 3

All autos have a floor cord working from the destructive battery terminal to the physique, to the engine, and from the engine to the firewall. Your project is in all probability a nasty gasoline sending unit. They fail greater often than the gauge.

Answer 4

posible loose sending unit wire

Answer 5

no idea