ive got a 1997-1998 volvo s 90 which has given me a few problems this yr but has been resolved except for the problem of my gas guage. its pretty much always giving me a reading of 3/4 to full at all times, even right before i fill gas of 17-18 gallons. i now use one of the gauges that tells me my distance since the last gas fill up. once i hit around 230 miles i fill all the way to ensure that i have at least 230 miles of driving till my next fill up. im not sure if its the guage - electrical problem or the floater, that has to be fixed or replaced. any help would be great.

My guess is the sending unit in the tank.

But try to get a wiring diagram to verify the wiring is ok.

I agree with 'Tech'. It sounds as if the 'float' is hanging up and not giving the proper reading when the tank is below the point at which the float 'binds'.

A 'sending unit' in the fuel tank sends an eletrical signal to the fuel gauge on the dash. The signal is just resistance to ground. IIRC (If I Remember Correctly), the resistance increases as the float lowers. I point this out because if the gauge works properly between the 3/4 mark and full then you don't have a wiring problem. If it doesn't, then there can be a problem in the wiring between the gauge and the tank (I doubt it from the way you are describing the condition). If the sender wire was shorted directly to 'Ground', the gauge would always read full.

When I used to work in a repair shop, I remember when a body shop had put a floor jack under the fuel tank and tried to jack up the car. If I were you, I would give a quick visual inspection of your fuel tank, just to see if it is distorted 'inwards'.