Workings of fuel tank gauge -

[peterme]

I have just filled the fuel tank of my 2002 M270cdi right up to the top - only to find that the fuel gauge registers 3/4 tank.

Why should this be? Is there an old-fashioned float in the tank that has jammed - and if so, what should/can I do to free it? Alternatively, is this likely to be an electrical fault?

Advice would be welcome!

[Gilly]

I'm surprised no one has had a problem like this before (that has posted about it anyways).
There are a few wierd things going on with the fuel monitoring system on the ML's, at least for the last few years, not sure if it was from the beginning of production or not.
Essentially what you have is a system that monitors the actual fuel level for only the first few liters of consumption out of the tank, using the traditional float method. They changed the quantity of fuel it uses a couple times, but I believe it was first just like 3 liters, then changed it to 10 liters. Don't quote me on the amounts.
Anyways, after it used up a certain quantity of fuel, it would then STOP using the traditional method of fuel level monitoring and instead starts using the engine control module to calculate the amount of fuel being consumed and detracting that from the fuel level reading, what they call a "virtual calculation".
One problem they were running in to was with people who wouldn't burn off that first quantity of fuel before filling up the tank again, so if for example you vehicle was set up to use the "actual reading" method for 10 liters, and you filled up after only using 9 liters, it would throw the whole thing out of whack, you may fill it up for example at that point and the gauge would mysteriously drop to "zero fuel". Ain't that neat?
The "real" fix (irregardless of what kind of hoops MB tries chasing you through) is to disable this whole "virtual calculation" BS. It can be changed in the instrument cluster (with the MB shop computer, SDS) to operate only off of the actual fuel level sender, and it'll work great. I hope this helps, this is info all based on gas engine ML's here in the US, hope it applies to your Diesel.

Gilly

[peterme]

Gilly -

Many thanks for your prompt and very helpful reply. Much as I love my MB truck, there are features - like this tank gauge - that make me think that the design engineers overdid things. I hope to heck that the local MB workshop guys are able to recalibrate the thing.

Best regards

[ljcml]

Check out the pictures of the fuel gauge assy on "wolfgang's ML page". If the lever on the float is rotated a certain way, the thing can't come to the top even when the tank is full. Mine does the same thing: you fill up to the brim and it shows about 7/8 full and doesn't move for about 50 miles. It's not a big deal, just another assembly detail that can vary from one ML to the next.

[peterme]

A quick update on that fuel gauge. Having been through two cycles of filling the tank right up and getting a 3/4 full reading on the gauge, I ran the fuel level down pretty low - only to find that on filling up on the tird occasion that gauge seems to have corrected itself automatically...

[itb76]

For whatever it's worth, our '98 ML320 VERY rarely reads a full tank, even if you top it off a couple times. 7/8 is pretty typical. However I can attest to the accuracy of the gauge at the other end of the scale. When the gauge reaches the bottom, it's empty!

[wingrove]

Where do i find "Wolgangs ML Page" ?

[Ron in SC]

Wolfgang website, and an excellent one it is, see below link.

http://www.whnet.com/4x4/index.html

[azinn]

Originally posted by wingrove
Where do i find "Wolgangs ML Page" ?

I believe this is what your looking for here http://www.whnet.com/4x4/badgas.html

[Q]

Speaking of funky fuel levels. I just inherited a Buick that registers full for the first 100 miles and then exponentially accelerates toward E. I swear from 1/2 to 0 is like 80 miles and F to 1/2 is the other 200. I'd take my ML's method any day of the year.