Join Date: Dec 2002
Location: Saint Louis, Missouri
Re: Fuel sending unit
I would think with 9 gallons in a tank the meter should read about 45 ohms (on an 18 gallon tank).
You should be able to figure what the meter reads by knowing what the range is of the sender (0-90 ohms) and the size of the tank.
If you have a 20 gallon tank and have 20 gallons of fuel in it the sender should read 90 ohms. If it only had 10 gallons then 45 ohms, and empty 0 ohms.
If you had a 16 gallon tank then 8 gallons in would be 45 ohms, 16 gallons 90 ohms, and empty, 0 ohms.
I would tend to think that even with 2 or 4 gallons in the tank you would want the sender to measure 0 ohms so that in your mind when you see the gauge on empty you still have some fuel to get to a gas station.
When I test 0-90 ohm GM fuel level systems I use some resistor values close to 22.5 ohms for checking the gauge to see if it reads 1/4 full tank. I then swap in a resistor close to 45 ohms to see if the gauge reads close to half full. I then tie the 45 ohm and 22.5 ohm resistors in series to give me 67.5 ohms to see if the gauge reads close to 3/4 full, and then either use two 45 ohm resistors in series or a resistor close to 90 ohms to see if the gauge reads full.
1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)
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