It occurred to me that the fuel float will get "pinned to the ceiling" when the fuel is closer than 10-15mm from the top. That explains pretty easy why the measurement will max out at 82L. Damn laws of physics keep messing with us. maybe they could use a pressure gauge at the bottom to measure depth to get top to bottom reading (similar to plane altimeter)


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This 82L number corresponds to what my IBUS app indicates as fuel level when I totally top off my tank.

Mike

I haven't driven much since the I changed the float arm angle, but I'll be filling up from two thirds (displayed) and see how the numbers match up.

In any case I think I'll still change the whole assembly at some point in the coming months to play it safe considering my future plans with the car

https://www.dropbox.com/s/f2uqckbs8g..._4236.MOV?dl=0

I recorded fueling with OBC #6 turned on. Maxed out at 82L while the pump clearly showed I filled up 24gal. Could there be something else, I am surprised an over engineered German car will allow this much discrepancy

https://uploads.tapatalk-cdn.com/201...952a4a3ef7.jpg
https://uploads.tapatalk-cdn.com/201...9232521c27.jpg
https://uploads.tapatalk-cdn.com/201...37deae0091.jpg

My ibus indicates 82l fuel, when I top of the tank.


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e53 Fuel Supply Detailed (fuel pump / siphon pump diagnostic help)
 

It actually makes sense. Watch the dial as you drive. The first 10L of consumption doesn't move the gauge. In other words the top 10L is "off scale". I think the car assumes you fill it up whenever the gauge doesn't bobble from 82L.

It would take some alien tech to avoid the problem.

I'll draw a diagram to help explain:

https://uploads.tapatalk-cdn.com/201...35746b6d92.jpg

Laws of physics dictate when you have a float some portion will be above and some below the level of the fluid.

When the float is at the bottom it is possible to more or less be able to measure the bottom as there is zero liquid and the float no longer does.

However web at the top, the float will hit the top of the container and stop rising for the last cm or so. That works out to about exactly 10L of fuel.

It's crazy that this has only been discovered in 2017! Silly "everybody on planet Earth" for assuming that the gauge on our cars went from 0-100% when they really go from about 5 to 92%.

"Everybody" knows that the first 50-80 miles the fuel gauge doesn't move. Now pretty much exclusively the few people to read this thread and the actual designers of the fuel gauges know why.

The float is pinned to the top of the tank from about 92 to 82L in the case of the E53. The fuel gauge will be pinned at 1/1 until you consume about 10L at that point the computer will read 82 L and dropping and the needle will start to drop.

I'm not aware of any other sensor to confirm the tank is actually full so if you only filled to 84L I'm pretty sure the computer will over estimate your range and make an abrupt adjustment when the floats are no longer pinned to the top.

My test showed that my computer saw 82.0L for the first 60 miles or so then finally started to drop absolutely confirming what I've described above.

The tank could be made with a bump in the top to make room for the float but that would reduce the capacity of the tank by lowering every place besides the float bump. It's a reasonable trade off and every car on Earth does the same thing just the 0.001% club now knows why.

I will try to fill it up today, and take it for a drive to see how long it stays on 82l


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Just to se iff the missing 10l is the top of the fuel tank


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It will absolutely a guarantee! What you will see if you have test six live is that when you get to about 8-9L consumed, the levels will bobble around when you take hills or curves but still settle to 82.0L.

Once you get to more than 10L consumed the test six total will finally start to drop.

The computer is smart enough to assume you filled up so the averages and DTE still calculate based on 92L it doesn't wait until you get to actual 82L to start counting down.

Everybody should check their test six both when full and empty periodically.

Apparently when I replaced my pump recently I put it in crooked or something because my right sender only goes down to 5L or so throwing off my DTE. (it shows about 3.5L more than it should). I will be exploring the situation using a fiber optic camera from the left tank opening to determine what I goofed to share with the group.


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While I'm 100% sure you are correct on this, I'll have to take your word on it. The "Range" value (or DTE as you call it) is only three digits and mine is pinned at "999" for the first few hundred kms of driving after filling up. :D

Actually, if I bothered to switch to miles, I'm sure it would show a value I could see decrease right from the first drop of fuel. 1,300kms is about 808 miles, well less than the maximum Range (DTE) value of "999". ;)