fuel gauge incorrect after engine replacement

[Sparticle]

Howdy folks. 1997 Subaru Outback. We had the engine replaced and now the fuel gauge shows empty when there is still 5 gallons left in the tank. This is different than it was before the engine replacement. It measured correctly before the engine replacement. Simple fix? What's up? Thanks.

[fishhead]

My gas gauge went bad but in the opposite direction. My mothers neighbor was a mechanic and he said it might be the ground wire from the pump.

[OkieDavid]

Interesting question- Unless you also changed the fuel tank I can't see that an engine replacement had anything to do with it since the "sending unit" is inside the fuel tank.

[Danaus29]

I wonder if the tank was tipped and isn't setting where it is supposed to.

[Bluecometk]

Your Outback has two sending units in it. A main unit that houses the pump, filter sock, and low fuel thermister and main float assembly. The secondary side houses the secondary float and return line jet pump assembly. These assemblies are grounded through the ECM. Subaru’s have multiple grounds on them. Your vehicle has a ground on the right (Passenger) side if the intake manifold facing the rear. The next is mounted from the pitch stop to the top of the transmission (Dead center against the firewall) The main ground goes from battery to starter hold down bolt and a sub ground goes from the battery to the fender well. On certain production dates there may even be a ground going from the power steering line hold down on the manifold to the right side fender well and attaches to the pressure switch, sourcing solenoid. There are many more on the vehicle but performing and engine swap or rebuild would not bring the tech in contact with them.

You don't state how long after the engine job did the gauge start reading incorrectly. So I am going to make an assumption in that it was a tank or so later. That being said.

I personally think you have a sending unit going bad. They both share the resistance to the gauge and over time they get loose on the shaft and then create burn spots on the resister grid.
1996 to1999 model Outback /Subaru’s are known for this happening with the sending units from one tank full to the next, just out of the blue.
They are quite easy to remove and replace in your vehicle.

You can access them from inside the vehicle by folding down the rear seat backs, rolling or removing the cargo area rug and removing the two access hatches (Philips #2 driver) and then remove the 8mm nuts that hold the units in place. You will need to remove the fuel hoses (NOTE: REMOVE/DISCONECT THE LARGE SIX PIN ELECTRICAL CONNECTOR ON THE RIGHT SIDE UNIT FIRST, THEN START THE VEHICLE UNTIL IT STALLS OUT TO RELIEVE FUEL PRESSURE AND THEN LOOSEN THE FUEL CAP)

NOTE: IF YOU HAVE ANY TREPIDATION ABOUT DOING THIS TYPE JOB DON’T DO IT!!! LET AN EXPERIANCED DEALER TECH DO IT!!
They will have any needed parts on hand and have done it a million times.

These are just my opinions I hope they help.

Bluecometk

[Sparticle]

Well, Mr. Bluecomet man, you know your stuff! I think I can handle this myself. Thanks a lot.