Incorrect fuel gauge

I’ve posted a few times on here about my 1993 Hyundai Excel and based on the recommendations of the community I got it up and running and let me tell you it runs PERFECTLY. Previous owner put a new fuel pump in but used an unknown aftermarket eBay model and upon pulling it out I discovered it was cracked where the hoses run into it. I was barely making 14psi at idle. Replaced with a Delphi pump and I was good to go. Anyway, on to the problem I am having…

On this particular car, the fuel level sensor/float is not built into the pump assembly and is replaced separately without having to drop the tank. Well, my fuel gauge doesn’t usually go above 3/4 even after filling up and tends to go towards E relatively fast. It did this with both the old and new replacement fuel level sender I put in (which was OEM from Hyundai). All the wiring and connectors seem to be intact…I mean it obviously works enough to give me an incorrect fuel level. The only thing I can think of is maybe the fuel gauge itself is bad. The fuel gauge IS removable. As far as I know, the needles were never removed or tampered with. Am I on the right track or is there anything else I could look at? This isn’t a huge deal but I like everything in my cars to be functioning so it is something I would like to see fixed at some point. Thanks!


I presume you have access to the fuel level sensor . . . ?

If so, do you have access to a decade/resistance box?

If yes, you will need to simulate 1/4, 1/2, 3/4 and full tank

If the gauge will not read what you simulate, then the gauge or the wiring is the problem

If it will read what you simulate, the sensor is the problem

Here are some examples . . .

On many GM vehicles, 40 ohms is empty, and 240 ohms is full

On many Ford, and some euro vehicles, it’s backwards, with 3 or 4 ohms being e, and high resistance being full. I don’t remember the exact spec for full

I’m tentatively guessing the fuel level sensor is the problem

I’ve replaced far more faulty fuel level sensors, versus faulty fuel level gauges

I do have access, and have already replaced it with a brand new OEM part from Hyundai. Both the old and new fuel level sensors gave the same readings on the gauge so I didn’t suspect that the fuel level sensor was the culprit. The gauge does not work at all if it is unplugged.


In that case, the problem might be wiring and/or gauge

Since it does move . . . incorrectly . . . the wiring may be fine

Do you have access to a decade/resistance box?

It would confirm that bad gauge rather quickly

I sure don’t! :neutral:

Even if you don’t have the resistance box, you could substitute a couple of cheap resistors, in place of the sensor

From Fry’s or Radio Shack, for example

Resistance boxes aren’t that expensive, either. Less than $100 and you’re in business, less than $50 if you’re not picky

After a few nightmares fighting less than perfect fuel gauge complaints I long ago quit worrying about the fuel gauges on my own vehicles unless by coincidence the cause became obvious while replacing the fuel pump if that ever became necessary. I found that filling the tank and zeroing the trip meter was a failsafe method to never run out of fuel. Was the Autobahn littered with VW Beetles in the 1950s when there was no fuel gauge on that car? Thousands and thousands of Europeans must have been as resourceful/lazy/cheap as me.

Early models of the East German Trabant had no fuel gauge. It had a gravity-fed carburetor with the fuel tank on top of the 2-stroke engine, which for Western standards made it a street-legal lawn mower :wink: . You used a dipstick to see how much fuel you had.

@“Rod Knox” A few years ago when gas was well over $4/gallon, a woman brought in her aged Buick. It looked like it had been rescued from the junkyard–bungee cord holding the hood closed, upholstery torn to shreds, duct tape holding up the window, etc. Her complaint was that the fuel gauge didn’t work properly and she kept running out of gas in dangerous spots.

We diag’ed a bad sending unit in the tank. The parts had long been discontinued but a NOS was found, at a premium price. Add on labor, a new pump I recommended, and a filter, and the price to fix it was north of $600.

I suggested that since her trip odometer worked, she could fill the tank completely, reset the trip and then fill the tank completely again before 200 miles. She would never run out again if she did that. Her response?

“It costs over $80 to fill the tank from empty. I can’t afford to do that all the time. I guess I’ll just have to get it fixed.”


Some people can’t be helped @asemaster.

About a dozen years ago the fuel guage on my '87 Olds started sticking when it got down to half a tank. Turned out the float inside the gas tank was broken.

A hairline crack in the float can be puzzling.

I remember the very first VW Beetles. They had no gas gage, but a small reserve tank which you turned on when you ran out on the main tank. I never understood the logic behind this, but it must have been cheaper than an elaborate float, sending unit, and dash gage. In 1946/47 German industry had not recovered yet from all the war damage, and early Beetles even had their roofs made form two plates welded together.

I’ve had two vehicles with misreading gauges.
On both of those I bent the rod to the float so as to read EMPTY accurately.
Never had a problem with that scenario after that.
I still have the 79 and you can drive around town for weeks with the gauge reading full. But when it starts to move you know you really have just half a tank and when it indicates getting close to empty…believe it or walk.