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Old 02-04-2014, 02:09 AM   #1
Boxster1971
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Default NCV3 fuel level calculated by consumption not fuel level sensor

I just discovered a little fact about how the fuel gauge works on my 2012 Sprinter. I suspect this is true of all NCV3 Sprinters. According to the option code description of Sprinter NA – J51 Fuel level display adjusted for additional fuel requirements, this is how the fuel level display works:

“In the standard specification, the fuel level display in the instrument cluster is controlled solely by the fuel consumption as calculated by the onboard computer. The level is only reconciled with the fuel level sensor in the tank and corrected when a refuelling operation is detected. With this code, the fuel level display in the instrument cluster is reprogrammed so that it is solely controlled by the fuel level sensor in the tank, and shows the approximate amount of fuel remaining in the tank.”

This fully explains the experience I had last month of running out of fuel with the gauge reading half a tank after a large fuel leak from the fuel filter. It also explains why the gauge stated reading correctly (empty) when I added a couple of gallons to the tank.

I’ve attached the page covering this option code. My Sprinter does not have this option code J51 so my fuel level display is calculated on consumption and not the fuel level sensor. An interesting fact of Mercedes engineering to keep in mind for the future.
Does anyone have other info on this? The J51 option code was listed in the 2010 Option List, but is not in the new 2014 Option List.
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File Type: pdf Sprinter_NA-J51 Fuel level display.pdf (29.2 KB, 169 views)
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Old 02-04-2014, 03:17 AM   #2
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Makes more sense to me now.......I drive mine constantly down to reserve fuel and then at that point even further till the range won't display miles to empty......I go and fill up and it only takes 23 gallons....lol. This is every time. I have never pumped 24 gallons in and I've driven 30k miles so far
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Old 02-04-2014, 03:19 AM   #3
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

The Sprinter service writer at my MB dealer has mentioned refrigerated body Sprinters running out of fuel when the gauge indicated fuel remaining. I wonder how the consumption is calculated. If by a gross flow device it would have counted your leaked fuel. Do you think that it measures electronically the fuel based on the computer firing the injectors or possibly actual flow into the high pressure common rail injection system? I am on my second NCV3 with an Espar heater. I am aware of the problem but have not detected any "error" as the heater uses so little fuel between my refueling times.

Edit: These refrigerated systems use fuel from the auxiliary tap on the tank; they are not compressor driven by the engine.
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Last edited by Diamondsea; 02-04-2014 at 03:22 AM. Reason: Add last sentence.
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Old 02-04-2014, 08:41 AM   #4
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

With the High Line dash I've found that the remaining mileage value disappears altogether once it drops under "20" and is replaced by a non-cancelling "RESERVE" message. However going by what I then see at the pump I actually think the true remaining range is more like "40".

Something else I've noticed on mine is that it takes quite some time to establish the current fuel consumption value compared to manual transmission variants (mine is an auto). Can't explain why this is, it just is!
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Old 02-04-2014, 03:24 PM   #5
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Quote:
Originally Posted by Diamondsea View Post
...If by a gross flow device it would have counted your leaked fuel. Do you think that it measures electronically the fuel based on the computer firing the injectors or possibly actual flow into the high pressure common rail injection system?
My leak was at the filter on the low pressure side and I know that fuel at this pressure is also returned to the fuel tank. The actual fuel injected is calculated by the CDI Control Unit using multiple sensor inputs. See attached Sprinter Overview Slides on the CDI Control Unit, especially the last slide on Mixture Formation.

This is same info that gives us GPH of fuel consumed on the OBD II connector that we can see on a device like the ScanGauge.
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File Type: pdf 2010 Sprinter CDI Control Unit.pdf (621.2 KB, 44 views)
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Old 02-04-2014, 04:20 PM   #6
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

In my very short experience, the low-fuel indicator is completely off. According to the manual it should come on when there are 5 gallons left. Mine comes on somewhere between 7-10 gallon left. MPG has been very consistent (always between 20 and 21), so consumption-based calculation don't explain what I see.
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Old 02-04-2014, 06:57 PM   #7
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Quote:
Originally Posted by Diamondsea View Post
... I am on my second NCV3 with an Espar heater. I am aware of the problem but have not detected any "error" as the heater uses so little fuel between my refueling times....
Agree that your Espar heater uses so little fuel that you would not notice since the level is in essence recalculated when you add fuel to tank. I could see this would be a problem for a system running a diesel/electric generator for long periods of time in between refueling. Also the diesel drive refrigerator systems you mentioned as they likely run continually.
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Old 02-04-2014, 07:53 PM   #8
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Wow! Don't install a diesel generator!
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Old 02-05-2014, 01:55 AM   #9
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Since MB offers the option of having the fuel gauge respond directly and only to the tank level sensor do you supposed that RV up-fitters order that option? Many RVs may use diesel gen sets and not propane. Are there RV up-fitters reading this? What do you order for your cargo vans or cab-chassis?
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Old 02-05-2014, 11:53 AM   #10
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Default Re: NCV3 fuel level calculated by consumption not fuel level sensor

Great find!

This is not related to NCV3, but I wonder if there is some of that going on in my T1N too? A couple times I have filled my Sprinter while the engine was running. Those times I noticed that the fuel gauge didn't respond to the added fuel. It did eventually correct, but not right away. I just wrote it off to signal damping. Maybe more is going on.

Back to NCV3.
I can see where this "feature" could mess up a refrigerated truck powered by diesel. That is a heck of a lot more fuel consumption than a little D5 Espar heater.

This might help to explain some of the discussions there have been here about "Reserve" amounts and tank size.

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