Fuel gauge problem?

[mnm99]

When I fill my car up it goes to full. After driving around the gauge will go down to 1/4 then go back up. It does it at random times. I checked the connections on the sender. All good. I checked all the connections on the gauges and there tight too. I know there is a 12v to 10v relay. Is this the one? It reads 12.2v on one side and 11.8 on the other. Is there anything else I should look for or is prone to happening?

Thanks. #467

[Mark IV]

You need to check the ground from the fuel sender to the chassis. The sending unit reads "full" at ground. It is 250 Ohms empty and 20 ohms when full. Ground the sender to the negative on the battery and the guage should read "full".

Likely a bad sending unit, but check the ground first. The rheostat winding gets fouled from the ethanol fuel so they "short" in one spot and thus it reads correctly until it hits a bad spot and then grounds to read full.

[mnm99]

I think I fixed it. The voltage stabilizer was touching metal. It sounds weird, but it's not mounted behind the dash to a solid point and whenever it touched a piece of metal the gauge would drop. like the body of it was grounding out. I wrapped it in tape and tie wrapped it now it's all good.

Edit...I thought it was good. It's doesn't jump around, but I think it's not the correct level. Like I mentioned it has almost the same voltage on both terminals. I want to make sure this is the right part before I change it out. I'm not getting my 10V on either side for sure.