Gas gauge - digital vs analog

This evening my analog needle was near the "E" (gas light came on) while the digital "gallons used" was showing 30.8 indicating I still had (in theory) 5+ gallons left.

Up until now, the digital and analog had been pretty closely aligned along the way.

So when I filled up, the amount on the pump showed 31.8, which is well within the standard deviation of my past fill ups compared with the digital.

What has been more accurate for ya'll's fuel consumed......digital or analog?

Also should it be a concern that my analog was showing almost Empty when in actuality I still had over 4 gallons left in the tank?

Go by the lower read to fill er up

TornadoRaptor said:

Go by the lower read to fill RR up

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Sorry but what does RR mean?

I filled up because the gas light came on, but it filled up at 31.8 gallons, which is well short of the 36 capacity. I would have expected it to fill around 34 or 35 gallons.

RaptorEnthusiast said:

Sorry but what does RR mean?

I filled up because the gas light came on, but it filled up at 31.8 gallons, which is well short of the 36 capacity. I would have expected it to fill around 34 or 35 gallons.

Click to expand...

Typo.... I typed er

as in fill her up

Big fingers

I am willing to bet that the digital figures are derived/calculated by the computer and the analog reading is from the float sensor in the fuel tank. One discrepancy does not necessarily a problem make, but if that discrepancy persists it may indicate that you have a software or firmware glitch in the ECU.

Ruger said:

I am willing to bet that the digital figures are derived/calculated by the computer and the analog reading is from the float sensor in the fuel tank. One discrepancy does not necessarily a problem make, but if that discrepancy persists it may indicate that you have a software or firmware glitch in the ECU.

Click to expand...

Thanks Ruger. I will also add that yesterday happened to be the day I switched to stock tune before I took it in to the dealership for oil change and tire rotation.

Then I switched it back to performance tune in the afternoon prior to filling it up. Could that affect the discrepancy?

Also generally, which should be more accurate? The computer derived or the floating sensor?

Thanks

David

@raptorEnhusiast, run a cheap experiment. Take that tune off, return the truck to the factory tune, and then run it for a couple fill-ups to see if the two fuel indicators agree.

IF I'm right that the digital readout is calculated by the ECM, it's based on engine size, fuel tank size, ECM-recorded driving habits, elevation above sea level (air density) - everything the sensors send to the ECM. Sounds impressive, but it's calculated based on the ECM's software. If you want to know miles-to-empty, that's good info. BUT if you want to know how much fuel in gallons is in your tank, the float sensor measures that directly.

The light is for 'low fuel' not 'no fuel' usually that allows for about 40 miles of driving to find a gas station or about 4 -5 gallons. The light coming on with 1 gallon left is cutting it pretty close. I personally don't like to run that low of a level on a normal basis since the fuel pump uses the fuel in the tank for cooling purposes. A guy I work with has put 3 fuel pumps in 2 years in his wife's Expedition because she always runs on the bottom of the tank.

In my truck, the light usually does come on with about 40 miles left. While I don't normally run my truck that low, the few times I have, it has always had about 3 to 4 gallons left. Figure the low side 11 to 12 MPG, 3 to 4 gallons, yep bout right.

The needle is more accurate to what's in the tank because it's reading the float level.

The light and miles left are computer generated, by the MPG readings.

On my 2010 1/2 the light and fuel stations on the Nav come on at 50 miles left.
Now if I'm getting 7.8 or 11.2 the needle well be in different spots.