I had to have my "fuel sending unit" replaced last October. I would fill up my tank and the very next day I would be at the mid pt as far as the gas gauge goes...so the dealer replaced that and the fuel reading was no longer erratic.

My question is whether the Fuel Sending Unit is the same thing as the O2 sensor? I heard replacing your O2 sensor can improve gas mileage by up to 15%...any one know about either of these 2 things...or it if they are the same thing...

 

The fuel sending unit looks like this and is located inside in the gas tank.

It uses a float that moves down as the gasoline in the tank goes down. It converts the travel of the float into electrical voltage, and is sent to a special metal spring that's attached to the fuel gauge. This metal spring is sensitive to varying voltage, and is how it moves the needle. Fuel sending units become inaccurate because they develop excessive resistance in the circuitry, which to the gauge reads as lower fuel level.

I'm not sure exactly how an O2 sensor works, but I do know it's used to provide feedback to the ECU as to how the emissions of the engine are. On OBD-I vehicles, there is an O2 sensor mounted on the exhaust downpipe. OBD-II vehicles also have a second O2 sensor mounted in the catalytic converter to measure the efficiency of the cat. A common problem that causes the "check engine" light to come on is a faulty O2 sensor, as to whether replacing it will improve gas mileage, it couldn't hurt

 

WOW. I have the same fuel problem in my 93 accord and I thought I would just have to live with it. I can fill it up and at 50 miles its at half a tank. But it stays there till about 160 then works fine the rest of the way down.

 

If you pull your fuel sending unit out, you'll see the device that converts the travel of the float into an eletrical current, located about halfway along the unit. If you take some q-tips and wd-40 you should be able to rub off a lot of the corrosion on the device, you'll see what I mean when you look at it. Also, I sanded down the ground point located in the trunk just in case it was causing some un-needed resistance.

 

All sounds good, but be very careful with that stuff. If you do any kind of sanding on that rheostat wiper, or get anything messed up, you want to make sure it can't possibly cause any arcing. Sparks inside the gas tank are usually NOT a good thing.

 

just sand the ground point of the unit, it's grounded outside of the gas tank. . like this