Gauge Signal Fix for Fuel Cell with GM Sending Unit

[solallein]

Ok so the GM sending unit has a resistance range from 0-90 Ohms and in my 1995 240sx the stock sending unit is 4-84 Ohms. So everything should be gravy right? Just solder a couple wires and your ready to go right??? Nope. The resistance is inverted in the GM sending unit so that when its full it'll be 90 Ohms when the stock 240 sending unit would read 4 Ohms.

Note: The fuel cell that I got has a sending unit that is not easily removed.
How to fix this crap.
Option 1:
Get an aftermarket fuel gauge and wire it up.

Option 2:
Make a difference amplifier that will correct the voltage drop by subtracting the voltage coming out of the sending unit from the voltage going into the sending unit and then sending this new voltage to the gauge.
What you will need:
4 1k Ohm resistors
1 Op amp
1 Perf board solderable
1 Enclosure
Cost ~$5-10
Wire and soldering iron
Estimated Time <2 hr

Follow this schematic where Eout = E2 - E1

Here is a schematic for the op amp. Notice that its upside down so don't get confused, and Vs+ will be the voltage supply going into the sending unit and Vs- will go to ground.

If you don't understand the schematic just do some googling and learn.

[compactfean]

Just use modded 240sx sending unit? Lol, I swear sometimes.

[solallein]

Yea if I could have I would have. Guess I'll edit to stipulate that