Just saw that I had two messages, I hope this is replying.
I don't know what empty ohms is equal too. And I am about 2400 miles from my car
What you can do is get a variable resistor, 10 turn, 20 turn, etc from radio shack. the fuel gauge is just an ammeter. so if you connect the multiturn potentiometer with one leg to the fuel gauge and the wiper to ground you will see the gauge change as you add resistance to the circuit. When the gauge reads full, remove the potentiometer and measure the resistance. this will get you rather close.
variable multi-turn pot, radio shack Potentiometer/TrimmerModel: 271-343 | Catalog #: 271-343
http://www.radioshack.com/product/in...ductId=2062308
Way more resistance than you should need so you may be turning several times before you see something happen.