Thread: Fuel guage is lying, 300tdi 110

Hi, I have had a new tank and fuel sender fitted recently and found the other day that the sender is lying. With the needle in the middle of the red zone the thing started spluttering, short of pulling the tank back out and bending the sender float arm I was thinking of putting a variable resister in series with the sender so I can recallibrate the guage to be acurate. Any ideas ?

Steve

As John just mentioned, check your ground on the sender first, and run a seperate ground wire to the chassis if necessary The gauge works by measuring a relative resistance between a 12v baseline and ground, and I've seen installs where the installer assumed that the sender would ground through the tank and the gasket played havoc with this.

More than likely though, you will need to adjust the sender. Putting a resistor in series with the sensor will (assuming you pick the correct resistance) correctly show when the tank is empty, but will never show when the tank is full. To illustrate this, consider the following data:

The stock Defender sender in my tank measured about 360 ohms empty, and 16 ohms full. If your sender is hitting the bottom of the tank too early, which it would be in your case, then the resistance range of your sender would be (say) 300 ohms empty, 16 ohms full, giving you the false reading on your gauge. If you put a 60 ohm resistor in series with this, then the "empty" resistance will now be correct (360 ohms), but the "full" resistance will be 76 ohms, and will never go lower than that no matter what you do - your gauge will never show your tank as being full. If you're happy with that, then so be it, but if you want accurate readings across the board, you have to physically adjust the sender.

The best way to adjust your sender, in my opinion, is to take the gauge out of the dash, wire it straight to a battery beside the tank (it's three wires, +, - and sender), bend and check, bend and check. The thread that isuzu110 linked to is basically me doing exactly that a few weeks ago.