Didn't find any reference to the fuel gauge in the FAQ's. I am replacing the prepump on my 740 turbo sedan project car. The fuel gauge does not work and I am at a loss as to a reasonable troubleshooting procedure.

Is there a float enclosed in the 2" diameter plastic tube portion of the sending unit? Things are pretty gummy around the prepump and its connections- perhaps this is also inside the tube and has caused the float assembly to stick? Sould I hear some type of float movement when I invert the assembly? I don't hear anything.

I am not anxious to explore this device without some insight from someone who has been there before. Anyone have advice or suggestions on trouble shooting? Thanks.

Randy

The easiest way to test the sender unit when it is out of the tank is to check the resistance with an ohm meter between the gauge connection and the body of the sender unit while you tip the assembly between upside down and right side up.
It should vary between approximately 40 Ohms upright and 250 Ohms inverted.

The sensor inside consists of two rods with spirally wound resistance wire and a float with a "U" shaped contact attached which bridges between these windings.

If you look closely at the assembly you can see the small barbs that need to be pushed in to unclip the outer tube and expose the internal workings.

It sounds as if the float on yours is, as you suspect, gummed up and sticking.

Colin.

1990 740SE B200E/M47, remote C/Locking.

Colin,

Thanks for your response. You are correct that the float was stuck. After spraying some electronics cleaner into the tube and washing it out the float came loose. I did in fact put a meter to it and found that the sender was giving varying amounts of resistance. I resoldered the wires I had cut to get that portion of the assembly off and connected the power (and ground) to find the gauge registering.

Randy