Fuel Gauge Unreliable

2004 LeSabre.

When the fuel level goes below 1/4 tank, the fuel gauge reading (and miles range reading) become unreliable and fluctuate slowly. It will slowly climb above 1/2 tanks, and sit there for a while or slowly drop only to slowly rise again.

Not many threads on this issue. Any ideas?

Just replaced the fuel pump in my 2000 lesabre. It comes with the fuel gauge sending unit and a pressure sensor for the tank. Wish I would saved it now and I could have sent it to you so maybe u could salvage out the fuel sending unit part out of it. Don't even know if u can do that, but pretty sure some of these guys do. The total cost for me was about 325.00 to have it installed which was much less than a dealer. I am fortunate and know a very good mechanic. It took him about an hour. There is an access under the mat in the trunk toward the front of the passenger side. Believe I could do it myself the next time if I have to. My fuel pump went out is why I had to get the new one. Would imagine that is what it is but u will hopefully be getting some good replies soon. Got some folks on here that are sharp on this.

I had problems with the fuel gauges on both of our 97 Lesabres. Turned out the sending units were bad in both cases. The sending unit is a variable resistor that reads between 0 and 240 ohms. Full is 240. If it reaches a quarter and then fluctuates some, the resistor in the tank is probably messed up. I installed salvaged units, but first tested by using a packet of variable resistors from Radio Shack. I disconnected the wiring at the tank and substituted resistors with known values. The gauge would read accurately for the values. A quarter tank would be 60 ohms approximately. Had to drop the tanks on the 97s, but I have heard the later models may have access through the trunk. Another test is to hook on a digital ohm meter to the wire that runs to the computer and move the float arm up and down. This can be done to read the resistance. More than likely though, it is a problem with the sending unit.

Thanks.
$140 at RockAuto for a new Delco sensor unit.
On the 2004 access is through the trunk floor.
Must be it has been a common enough issue to add the access cover.

The salvaged units included the fuel pump also and they ran around $100. It all went in as one unit with the sending unit and the wiring was intertwined somewhat. You might test the old unit with a digital voltmeter before removing it. Better yet, if you can touch/connect the wire from the new unit to the wire that runs to the computer, you can test the new unit before installing it. The key would need to be in the on position. Have someone watch the gauge. I installed one salvaged unit that was also faulty. It's great the tank does not need to come down. The strap bolts rust easy and the exhaust must be dropped out of the way.

Replace the Fuel Level Sender. Ordered part from RockAuto. It came with the new gasket.

Turns out the fingers that contact the resistance strip in the sensor were worn. This was at about 90,000 miles. See the attached photo for the failure point. I suspect a unit removed from a junker could show wear as well. Something to check

Replacement not difficult on the '04 thanks to the access port in the trunk. Some tips.
- The less gas inthe tank the better. Under 1/4 would be good.
- Be prepared to spill/catch some gas, up to a pint in the pump assemble, when you remove it. It takes a while to drain it and has to be position at several different angles to drain.
- The locking ring that holds the pump assembly in the tank is the most difficult if you do not have the recommended tool. I was able to work it off using large channel lock pliers and a lot of patience. Be careful, stray sparks from metal on metal could ruin your day.
- Use a bit of clean oil on the new gasket.
- Clean the locking ring and put some oil on the surfaces that will slide to lock in place to ease re-installation.
- Note that the pump assembly has a plastic tab that fits in a keyway in the tank top to ensure the outlet points in the right direction.
- If you have all the right tools handy, should take no more than 30 minutes plus cleanup. However, if you have to do it with with channel locks, and hunt for other stuff it can take substantially longer.