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Needed
Solder /soldering iron
Heat shrink
Resistors- radio shack
Wire cutters/ strippers
WARNING- This system has very low current, there little chance of shock, but either unhook you battery when possible or be very careful not to short out anything.
There are less YJ’s with accurate fuel gauges on this planet then there are unicorns, some can live with it, I could not, this walk-through should also work with XJ's with this problem
In a perfect world the potentiometer (sending unit) reads 0 ohms at empty and 90 ohms at full.
With 8 gallons in my 20 gallon tank my aftermarket sending unit read 15 ohms
Ideally I wanted to have 35 ohms at 8 gallons
(If you do this test, I recommend using exactly half a tank)
(Needle To Low)
Since my reading was 15 Ohms which is less than 1/4(22.5 Ohms) of a tank and I had 8 gallons in the tank
( 8/20= 40% full) 40% of 90 ohms is 36 Ohms
My true resistance should be around 35 Ohms
So I wanted to add a 20ohm resistor (using Ohm’s law of series: Resistor = Total Resistance -Sending Unit)
[EXAMPLE]
In my case (series: resistor = 35-15) solve for resistor and you get 20 ohms.
(Needle To High)
Alternatively if you resistance is too low, you could add a resistor in Parallel, and to figure out the resistance needed you need to use Ohm’s law of parallel circuits
Resistor = 1/ [(1/Total Resistance) - (1/sending unit)] solve to determine the resistor needed.
[EXAMPLE]
If you’re sending unit was reading ¾(60 ohms) of a tank when you only had ½(44.5 ohms), then
(Resistor) = 1/ [(1/60) - (1/44.5)] and the resistor needed would be 172.5 ohms
Once you determine the resistor needed its simple to install.
1. Remove you gauge cluster cover, which is 6 Philips screws
2. Remove 6 more Screws to remove the actual Cluster.
3. Find Fuel Gauge Wire
4. Cut wire/ Solder resistor in-between( for series )
I have a 94 YJ, some older YJ's will have a different cluster, but if you know which wire is for the fuel gauge it’s the same procedure
Here is my wire on my 94, the color was dark blue, and I believe the older style clusters use a tan wire, but referred to a wiring diagram to make sure.
If you want to double check you have the correct wire you can uses a multimeter to read the resistance of the wire you suspect, with the screw on the back of fuel gauge that is marked F, if you have the right wire it should read 0 ohms.
Once you have the wire, cut it, and turn on your key, you fuel gauge should go all the way to full. If it doesn’t then you probably cut the wrong wire Oo0oPS, fix and try again
Like so
Turn your key off, now you need to take the resistor you choose and solder it between the wire you just spliced (this will put it in series)
To put the resistor in parallel to lower the resistance you should NOT cut the wire, instead splice the resistor into the wire and then ground the other end of the resistor to the body.
Troubleshooting:
If you try these steps and it doesn’t correct your gauge problems there are a few things you can try.
1. Check the resistance directly at your sending unit; it’s best to have the sending unit removed so you can move the flow up-and-down while reading resistance to make sure that it is linear.
2. Fuel gauges do go bad, there is a technique to check the fuel gauge on the bench, and it requires 12 Volts and a few resistors or a working sending unit.
Finally to add, I believe the most important thing here is to know accurately when you’re going to run out of fuel, since every potentiometer responds different you may need to use trial and error (through replacing the resistor with one of a different value) to get your gauge to read E when it is empty. The equations in this post will give you a rough estimate within +/-10 ohms.
This walk-through would also be very helpful for someone installing an aftermarket fuel metering system that uses a different resistance.
Solder /soldering iron
Heat shrink
Resistors- radio shack
Wire cutters/ strippers
WARNING- This system has very low current, there little chance of shock, but either unhook you battery when possible or be very careful not to short out anything.
There are less YJ’s with accurate fuel gauges on this planet then there are unicorns, some can live with it, I could not, this walk-through should also work with XJ's with this problem
In a perfect world the potentiometer (sending unit) reads 0 ohms at empty and 90 ohms at full.
With 8 gallons in my 20 gallon tank my aftermarket sending unit read 15 ohms
Ideally I wanted to have 35 ohms at 8 gallons
(If you do this test, I recommend using exactly half a tank)
(Needle To Low)
Since my reading was 15 Ohms which is less than 1/4(22.5 Ohms) of a tank and I had 8 gallons in the tank
( 8/20= 40% full) 40% of 90 ohms is 36 Ohms
My true resistance should be around 35 Ohms
So I wanted to add a 20ohm resistor (using Ohm’s law of series: Resistor = Total Resistance -Sending Unit)
[EXAMPLE]
In my case (series: resistor = 35-15) solve for resistor and you get 20 ohms.
(Needle To High)
Alternatively if you resistance is too low, you could add a resistor in Parallel, and to figure out the resistance needed you need to use Ohm’s law of parallel circuits
Resistor = 1/ [(1/Total Resistance) - (1/sending unit)] solve to determine the resistor needed.
[EXAMPLE]
If you’re sending unit was reading ¾(60 ohms) of a tank when you only had ½(44.5 ohms), then
(Resistor) = 1/ [(1/60) - (1/44.5)] and the resistor needed would be 172.5 ohms
Once you determine the resistor needed its simple to install.
1. Remove you gauge cluster cover, which is 6 Philips screws
2. Remove 6 more Screws to remove the actual Cluster.
3. Find Fuel Gauge Wire
4. Cut wire/ Solder resistor in-between( for series )
I have a 94 YJ, some older YJ's will have a different cluster, but if you know which wire is for the fuel gauge it’s the same procedure
Here is my wire on my 94, the color was dark blue, and I believe the older style clusters use a tan wire, but referred to a wiring diagram to make sure.
If you want to double check you have the correct wire you can uses a multimeter to read the resistance of the wire you suspect, with the screw on the back of fuel gauge that is marked F, if you have the right wire it should read 0 ohms.
Once you have the wire, cut it, and turn on your key, you fuel gauge should go all the way to full. If it doesn’t then you probably cut the wrong wire Oo0oPS, fix and try again
Like so
Turn your key off, now you need to take the resistor you choose and solder it between the wire you just spliced (this will put it in series)
To put the resistor in parallel to lower the resistance you should NOT cut the wire, instead splice the resistor into the wire and then ground the other end of the resistor to the body.
Troubleshooting:
If you try these steps and it doesn’t correct your gauge problems there are a few things you can try.
1. Check the resistance directly at your sending unit; it’s best to have the sending unit removed so you can move the flow up-and-down while reading resistance to make sure that it is linear.
2. Fuel gauges do go bad, there is a technique to check the fuel gauge on the bench, and it requires 12 Volts and a few resistors or a working sending unit.
Finally to add, I believe the most important thing here is to know accurately when you’re going to run out of fuel, since every potentiometer responds different you may need to use trial and error (through replacing the resistor with one of a different value) to get your gauge to read E when it is empty. The equations in this post will give you a rough estimate within +/-10 ohms.
This walk-through would also be very helpful for someone installing an aftermarket fuel metering system that uses a different resistance.