Fuel gauge reading incorrect fuel level

[Eric0]

Hello guys! This week’s car problem isssssssss the fuel gauge is reading incorrect fuel level (always at full or close to full) I have an RB25DET wired to a S13 hatchback fuel sending unit.  I have double checked that the fuel gauge is grounded properly and connected correctly. So, next step was to check the fuel sending unit which I found is reading 0-2 ohm in both fuel and empty. So! That means it is reading the incorrect resistance. Is there a way I could fix this without buying a whole new sending unit, perhaps a resistor? 
 

Thank you all!

[GTSBoy]

The level sender is a variable resistor that is wiped up and down by the float arm. If it is reading a fixed resistance regardless of where the arm is, then either it is;

• Shorted close to one end of the winding,
• Really dirty in some way (although this usually results in high resistance, not low),
• Wiper broken off the arm so it is stuck in the one position,
• Any of a variety of other combinations of the above or something outright surprising.

Play with it. Work out what it is doing wrong.

[Eric0]

12 hours ago, GTSBoy said:

The level sender is a variable resistor that is wiped up and down by the float arm. If it is reading a fixed resistance regardless of where the arm is, then either it is;

• Shorted close to one end of the winding,
• Really dirty in some way (although this usually results in high resistance, not low),
• Wiper broken off the arm so it is stuck in the one position,
• Any of a variety of other combinations of the above or something outright surprising.

Play with it. Work out what it is doing wrong.

Hello! I cleaned it out with a cotton tip to hopefully get a better reading but the gauge still only reads from the range of full to 3/4. The board looks great, nothing looks physically broken, so I’m thinking the board doesn’t work electrically? 

[TerryP]

You should be able to measure the resistance change in the unit with a multi-meter.

You should expect to see:

• Between 4.3-6.3 ohms when the arm is fully lifted
• Between 27.7-34.3 ohms when the arm is around the half way mark
• Between 73.3.84.8 ohms when the arm is completely down

Taken from section EL-60 for Fuel Tank Gauge Unit Check S13

If the ohms reading on the multi-meter does not change then the unit needs to be replaced.

[Eric0]

3 hours ago, TerryP said:

You should be able to measure the resistance change in the unit with a multi-meter.

You should expect to see:

• Between 4.3-6.3 ohms when the arm is fully lifted
• Between 27.7-34.3 ohms when the arm is around the half way mark
• Between 73.3.84.8 ohms when the arm is completely down

Taken from section EL-60 for Fuel Tank Gauge Unit Check S13

If the ohms reading on the multi-meter does not change then the unit needs to be replaced.

I hace checked the ohm and it’s not reading anything. Where I love to get a new sending unit it’s $500 USD so I was wondering if there’s a part I could replace on the unit to make it read the correct ohms again?

[GTSBoy]

Isn't this what wreckers are for? There would have to be 15000 of these lying around on workshop floors here in Australia.

And no, you probably can't buy new replacement parts for the resistor coil in it. But here's the thing - do you know anyone who understands electrical stuff and can have a look at it to see why it's reading low ohms? It might just need a tweak.