Espar and fuel gauge

avanti

2022 Ford Transit 3500
So, this is interesting:
I vaguely remember reading somewhere that the NCV3 does not actually read the fuel level in the tank except during refills, relying on dead-reckoning from ECU information to compute remaining fuel while driving. I can now attest that this information is correct.

For the past few weeks, I have left my Espar coach heater running in our driveway, as an experiment. I occasionally turned on the key to check the fuel level, which started at 2/3. At first I was impressed at how little fuel the Espar was using--I couldn't even see the difference. Eventually, I started to get suspicious. This morning, I got a "lost flame" code from the Espar. Hmmm. Looked at the diesel feed line and it was full of bubbles. The fuel gauge was still showing 2/3. Well, well...

So, I drove to the gas station and filled 'er up, watching the needle as I did. After a few gallons, it suddenly jumped from 2/3 down to 1/4, and then started tracking the fill-up normally. I never did get a "low fuel" warning, even though I usually get it at 1/4 tank. The pump clicked off at 22.4 gal. So, there were 4 gallons left in the tank!

From this, I conclude two things:
1) The sprinter is oblivious to any fuel consumed through the aux tap; and
2) The aux tap (at least mine) goes a lot lower than the 1/4 tank that I was led to believe.

Worth keeping in mind if you are camping in the boonies.
 
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avanti

2022 Ford Transit 3500
That is interesting. But... how does the ECU know when the tank is being filled?
Good question. Obviously there is some kind of sensor, and it must not be just a binary trigger, since it has to work even if you are just topping up. I guess it could be something in the fill-pipe. Since the needle can track a fillup, I guess that proves that there is some kind of level (or in-flow) sensor. It just evidently isn't used while driving.

The fact that the needle didn't move until I got up to 1/4 tank is mysterious.
 
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smiller

2008 View J (2007 NCV3 3500)
I would have to believe that there must be a traditional fuel level sender (else how would you detect something such as a leak in the tank), and from parts listings a sender does seem to be present as an integral part of the fuel pump assembly, but it may be considered only one of several inputs when determining fuel level and perhaps not the primary one resulting in the calculation algorithm being confused by your fuel consumption while the engine was off. Maybe if you left the ignition on for a period of time the system would have eventually used the sender information to update the display? (just conjecture.) I think I read something somewhere indicating that the vehicle can be optioned to use the fuel sender as primary input, i.e. in an RV application where one would have to keep track of generator fuel usage, etc. Maybe someone with some more certain knowledge can chime in.

.
 
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avanti

2022 Ford Transit 3500
Maybe if you left the ignition on for a period of time the system would have eventually used the sender information to update the display? (just conjecture.)
Well, it didn't do so in the 5-mile drive to the filling station. Dunno.
 

smiller

2008 View J (2007 NCV3 3500)
Well it was designed by MB so whatever it does it does in the most complicated way possible.
 

johnshmit

Well-known member
It does read from the sender. Just got confused and didn't propagate the confusion to the arrow right away.
 

avanti

2022 Ford Transit 3500
It does read from the sender. Just got confused and didn't propagate the confusion to the arrow right away.
So, you think that I eventually would have gotten a "low fuel" alarm, but that five miles wasn't enough? Do you think it would have happened before I used up my four remaining gallons? (note that I had turned on my ignition numerous times over a period of weeks, and it NEVER updated the needle.)

The more I think about this behavior, the more nervous it makes me.
 

Boxster1971

2023 Sprinter 2500 144wb AWD
Avanti - in Dec 2013 I discovered that little fact about how the fuel gauge works on my 2012 Sprinter. I suspect this is true of all 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 explained the experience I had of running out of fuel with the gauge reading half a tank after the fuel leaks from the fuel filter messed up by a dealer. It also explains why the gauge started reading correctly when fuel was added to the tank. I posted my experience on this forum in Jan 2014.

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.
 

Attachments

smiller

2008 View J (2007 NCV3 3500)
Well that explains a lot. Apparently there is a fuel level sender but it is only used to confirm a fill-up, and if you have any kind of fuel leak (or usage other than the engine) the only way you know you're low on fuel is when you potentially run out in the middle of nowhere without warning. Brilliant.

I wonder what year this started?
 

avanti

2022 Ford Transit 3500
Problem Solved.

:cheers:
Well.... mystery solved.

But, I can still run out of fuel without warning. I am going to be careful. I can see the advantages of the ECU-based instrument. But, it seems crazy to me that it only recalabrates on fillup. Surely it should do so on every restart. Ah, the inscrutable German-engineer mind.:thinking:
 

JJolls

'14 170 4cyl Crew
I'm wondering if a dealer could adjust the computer to read it the other way... in effect, install option NA-J51? (for a small charge, of course!)
 

wmlog

New member
I see your point! You are very correct; the mystery is solved, but certainly not the problem. If you had a fuel leak, or just consumed it, say, with an Espar heater, you could have problems. You might actually have far less fuel in your tank than you thought! At least the Espar fuel tap doesn't go all the way to the bottom of the tank.

:idunno:
 

jme3505

2019 Gas Transit
Avanti - in Dec 2013 I discovered that little fact about how the fuel gauge works on my 2012 Sprinter. I suspect this is true of all 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 explained the experience I had of running out of fuel with the gauge reading half a tank after the fuel leaks from the fuel filter messed up by a dealer. It also explains why the gauge started reading correctly when fuel was added to the tank. I posted my experience on this forum in Jan 2014.

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.

This is interesting because every time I park my 2015 Sprinter uphill at my house the fuel gauge drops 2 bars. I'm not trying to argue but it's happened every time I park uphill. This is the same fuel gauge where the low fuel light turned on and it only took 16 gallons of fuel.
Jon
 

sailquik

Well-known member
jme3505/Jon,
It's NOT a "low fuel light".
It's a light that alerts you that you have used 75 liters of fuel (out of 100 liters the tank holds).
That's 19.8129 gallons out of a 26.41721 gallon tank.
You can easily use about 24-25 gallons and still have a little reserve.... I do it all the time.
Roger
 
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avanti

2022 Ford Transit 3500
OK, so I have another data point.
I was again in a situation like the one I described above: Starting with a full tank and parked in my driveway, I ran the Espar quite a bit over a period of weeks. This time, when I went to get fuel, I paid attention. Here's what happened:

Driveway:
milage: 17041
range: 404 miles
fuel gauge: full

Fuel station before fill up:
milage: 17045
range: 360 miles
fuel gauge: full

Just like last time, after adding almost exactly three gallons, the needle suddenly dipped down to about 2/3. I continued adding fuel, and the tank clicked off at 9.242 gallons.

Here is the new part: After the fill-up, the Range display showed 618 miles. So, although this confirms that the tank fuel level does not affect the fuel level needle, apparently it DOES affect the "range" display, which is good to know.
 

synergy_58

2009 Navion and 2015 Crew
So the display is a light bar, showing what we've used since the last fill up, computed along with the range to go, at the time of fill up, from that point. Right? What happens if we don't fill it all the way up and then we re-set the trip computer? And, then how does the display work, the one that always restarts at the beginning of the day, from the first run? I don't know what it's called, but the ECM recalculates new distance traveled, mpg, etc. every day, at the first start up for the remaining day. How then does this apply?

Every time I fill up, I reset my trip/mileage/mpg calculation, which I'm guessing the ECM must be doing automatically as well, for the fuel gauge. So what happens if I don't reset the trip settings manually, because I'm on a long trip and I want to establish my own manual MPG calculations and keep track of my travel mileage, say? The ECM is still going to reset the distance of travel based on my next refill, right?
:idunno:

On a side note: I have a diesel generator in my '09 Navion ('08 chassis), I've noticed that this application seems to be more accurate in its readings than my wife's 2015 gauge. The Genny will not start up if the tank is below 1/4 full, or close; however, if the Genny is already running, and the tank is going to go below 1/4 full, the Genny will continue to run for a while, but eventually shut off at a lower point of fuel level. It's weird. I tested this too, letting it run for as long as possible. The Genny shut down when the tank gauge looked like it was dead on empty. Then I drove about 3 miles and filled the tank and it took 24.6 gallons! So, it left me with barely enough fuel to get to a refill.

From all of this, am I now to understand that, with my new Espar in my wife's '15, I'm going to have to be my own monitoring system, manually?

:idunno:

Oh well, I guess it's just another strange quirky function of owning a Sprinter. LOVE IT! :bounce:
 

danski0224

Active member
Any feedback on the earlier question about whether or not the J51 option is dealer programmable?

I recall another thread where the fuel tank was punctured and it wasn't known until the van stopped when the fuel ran out. This calculated fuel readout really doesn't make any practical sense.
 

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