How do repair the fuel gauge that only indicates ¾ full when the tank is completely full? This problem has been getting progressively worse. I recently replaced the fuel pump and my mechanic and I inspected the sending unit which appeared to work fine. The float lever arm has free and smooth travel along its entire range. The float is made of a solid styrofoam material so no gas has seeped into it, which use to occur with the old hollow plastic ball floats. Is there some electronic relay that is wearing out? I thought of taking the fuel gauge out and when the tank is full manually moving the needle to full; however, this may damage the fuel gauge.

 

If you disconnect the level sensor lead (anywhere in the circuit) the gauge should read FULL or beyond. The gauge will interpret 0 ohms as an empty tank, and 90 ohms as a full tank. My suspicion is that you have some extraneous resistance to ground in the circuit somewhere, likely due to corrosion.

 

Also, those styrofoam floats DO get gas seeped into them after awhile.

If the margin of error has been steadily droppin the level on the gauge, I would suspect that.

I would have changed it when I did the fuel pump regardless of condition. This is really common on these cars, and it sucks to get back in there.

 

Ok, this is possible I guess. At least it is one thing to consider. I do not know if you can buy the float separate from the sending unit, if so then yes replacing it then the unit was out would have been prudent. Maybe the next best thing is to run the tank down one hot summer day and take the gas cap off and let evaporation remove any liquid from the float. However, this does have environmental consequents venting gas to the atmosphere. I watched as my mechanic removed and installed the gas tank. Not something I would want to attempt or pay the labour for again for this problem.