Fuel Gauge Reading Off

On a full tank gauge reads full after a.few.days of driving it will rapidly run down to half a tank at that point when I gas up it was actually at a 1/4 tank. I've read people say that ethanol has can cause this? What say you

 

I say your fuel gauge needs calibrated

 

Make sure all the wiring connections are tight and clean. The reading is regulated by resistance in the circuit.

 

Yeah, if you leave it stand too long at a 1/4 tank or so it would gum it up pretty quick, but I would bet ya need to pull the sending unit and calibrate it to your gauge. Be sure you have a good ground on the sender, and the gauge.

 

FWIW my gauge is off. It is too much hassle to fix it. I hate dropping the tank

 

Mine hasn’t worked in a few years have the sender to fix but nah.

 

It is most likely the sending unit and poor ground connection

 

Year, model, equipment? It's important. All we can assume is that you own an intermediate or later Jeep, since you posted in that forum. No such info in your post, signature, or profile.

There's no fuel gauge "calbration" per se.

The inaccuracy could be in the gauge (less likely) or in the sender (more likely). Suggest you read this thread - Build A Gauge Tester - for some background. You don't need to build the tester, but the testing methods used will apply.

You could also read the TSM for your year ... whatever year that is!

To me, the ethanol idea seems extraordinarily unlikely. The density of the gas will change when ethanol is mixed in, and that could affect how high the float in the tank sits on the surface of the gas. This effect will be very very small, if measurable. Also possible that the ethanol would attack a plastic float in the tank, but then the float would sink, and that's backwards from the high reading that you see.

Cleaning the connections is always a good idea, but the most likely problematic connections are on top of the fuel tank (assuming you own an intermediate or later Jeep), and a pain to get to. See Zila's and Jeff's post above.

 

If you have a semi functioning Guage you're ahead of most, haha. Your ohm capable multi meter is your friend. Id start under the dash to see if you're getting correct readings. If I recall the pink wire to your fuel gauge is the sender. 10 ohms is full, 25 is half, around 70 is empty if my memory is correct. If the ohm reading and gauge match, move to the sender. You'll not love dropping the tank. Run it as close to empty before hand. Last time I dropped the tank I thought I was nearly empty. It was still over half full.

 

Jeep CJ Gauge Diagnostics (whitegauges.net)

 

Your not gonna believe this i filled up my tank the other day with non ethanol and the gauge is reading acurately

 

I don't believe it.

We need a scientific hypothesis to peer review.

 

I believe it happened, but I don't believe ethanol is the reason.

Anecdotal. Provocative but not proof, could be coincidence. In most cases the rationale comes before the proof, not the other way. Otherwise you're just randomly testing stuff and hoping to discover something (like alchemy).

 

Mine is accurate after a fill up every time. Always reads "Full" It's around half a tank where things go sideways.

 

I think the gauges are generally ok (except for the goofy CVR part), but the senders in the tanks seem to be both inaccurate and fragile/unreliable. Plus the aftermarket senders are a genuine roll of the dice. If you get a replacement sender, test it for reliable and accurate operation with your multimeter before it goes in the tank.

 

Me too, and I can do it from the driver's seat. It's big improvement over using a lit match to peer into the tank.

(Model T Ford owners often had commercially produced rulers graduated in gallons for each style of tank.)

 

My Jeep had this problem - the easiest fix I could devise was to run a wire from one of the sending unit mounting screws (through the same sheath the sending unit wire runs in) to the firewall up behind the dash, where it's grounded. The fuel gauge still doesn't read super accurately, but at least it now provides some indication that there's gas in the tank.

 

This is no kidding. I made sure to test my replacement out as well as I could. Found the wiper arm wasn't making contact right and the ohm readings were all over the place. Put more of a bend in the wiper arm which put more pressure on the little nub that rides on the coil. Now I get smooth and mostly accurate fuel readings.

 

Yardstick here...