MPG Adjustment Factor - Possible?

[EastExpert]

Hi there,

Using http://www.spritmonitor.de/en/ I collected my "brim-to-brim" re-fuelling data for analysis. The tool allows to calculate real fuel economy judging by real mileage and amount of fuel used, so gives quite precise figures.

Thus, I found out that my instrument cluster MPG figures are about 4-5% optimistic. E.g. 25 mpg real figure is 26.2 mpg by display.

My previous car, a BMW 528i, had a special engineering mode in its OBC (On-Board Computer). You could put MPG correction factor there and I managed to get the OBC to display very precise figures (down to 1% give or take).

I wonder if I can do the same on my Mercedes C180K '09?

Thank you for reading this.

 

[turbopete]

this may well be incorrect for your car. i just clicked on the link to that site and it seems to be set up for l/100km or mpg using US gallons. i could be wrong though. i use the same equasion you used to get on those stickers from shell petrol stations when UK pumps started to change from gallons to litres. 1 gallon=4.54 litres. i fill to the brim, say for example 34.86 litres used from last brimmed tankful over, say, 213.6 miles. i get a calculator (coz im lazy and its easier) and divide 34.86 by the 4.54 to convert to gallons and put this into the calculator memory (7.678414 in this case!) then i put in my mileage, and divide that by whats in the memory ie 213.6 divided by 7.678414 giving me the average MPG for that fill up or 27.818244 mpg (27.8 is close enough for me!)

try it and see how accurate your computer really is. or isnt, as the case may be!

 

[survey]

Checking brim/brim over the last 17K, my car computer is 5-8% optimistic. I also wish you could apply a correction factor to the car computer.

 

[Rory]

I regard the displayed MPG as a relative number, so I can see if I'm getting good or bad MPG.

I can't see that the actual number in absolute terms matters (apart from bragging rights ).

 

[EastExpert]

Checking brim/brim over the last 17K, my car computer is 5-8% optimistic. I also wish you could apply a correction factor to the car computer.

On a '98 528i you could do that without any diagnostic laptops and CDs. You just pushed the tripmeter reset button and waited coupla' seconds. Then using long and short presses you could just browse through various interesting numbers. Yet another mode when selected, would put you into R/W mode, where you could enter your MPG Correction Factor*1000, e.g. 1035 would mean reduce by 3.5% (/1.035). After correction the MPG counter worked with amazing precision!

I am sure a new Merc can do that as well, can't it?

Why do you need it... OK, for instance, I try to calculate how much petrol is left by range indicator. If let's say you have 150 miles is left, and you're doing 30.0 mpg then you got exactly 5 gallons of fuel, and you know how much you'll be set off by next refuelling. Me being me, trying to calculate everything in my mind...

 

[survey]

On a '98 528i you could do that without any diagnostic laptops and CDs. You just pushed the tripmeter reset button and waited coupla' seconds. Then using long and short presses you could just browse through various interesting numbers. Yet another mode when selected, would put you into R/W mode, where you could enter your MPG Correction Factor*1000, e.g. 1035 would mean reduce by 3.5% (/1.035). After correction the MPG counter worked with amazing precision!

I am sure a new Merc can do that as well, can't it?

Why do you need it... OK, for instance, I try to calculate how much petrol is left by range indicator. If let's say you have 150 miles is left, and you're doing 30.0 mpg then you got exactly 5 gallons of fuel, and you know how much you'll be set off by next refuelling. Me being me, trying to calculate everything in my mind...

Why would one need it? Well really if you have a computer then why not ensure it is accurate? Just mildly annoying, that's all!

 

[EastExpert]

Why would one need it? Well really if you have a computer then why not ensure it is accurate? Just mildly annoying, that's all!

If present, that should be a service (engineering) function, not an end-user, of course. This Beemer trick was an engineering function.
By definition the on-board computer should be precise and if it isn't, it should be considered a workmanship defect and be repairable by dealerships.

It's just I don't see any such function. May be service computer does that?

(Otherwise it's stupid... display economy down to 1/10 of mpg, and have an error of 1.2-1.5 mpg up -- defeats the purpose).

 

[survey]

If present, that should be a service (engineering) function, not an end-user, of course. This Beemer trick was an engineering function.
By definition the on-board computer should be precise and if it isn't, it should be considered a workmanship defect and be repairable by dealerships.

It's just I don't see any such function. May be service computer does that?

(Otherwise it's stupid... display economy down to 1/10 of mpg, and have an error of 1.2-1.5 mpg up -- defeats the purpose).

Otherwise its stupid? - Can't quite agree with that. It does give a relative mpg readout even if slightly inaccurate. Easy to knock a % off. But I agree with you that it ought to be possible to tweak the computer to make it accurate.

 

[duncanh]

Mine is about 10-15% optimistic.

This amount of error makes the computed mpg figure largely useless. The only benefit I get from it is to see if my mpg is going up or down under certain circumstances, eg cold weather, hot weather, effect of speed etc.

But I don't need a computer to tell me this, common sense will do.

On a tank of fuel where the computer tells me I have got about 60mpg, I get in reality somewhere between 50 and 55mpg.

I would welcome the opportunity to get this re-calibrated, but would not pay too much to get it fixed - it is not that important.

 

[EastExpert]

Mine is about 10-15% optimistic.

This amount of error makes the computed mpg figure largely useless. The only benefit I get from it is to see if my mpg is going up or down under certain circumstances, eg cold weather, hot weather, effect of speed etc.

But I don't need a computer to tell me this, common sense will do.

On a tank of fuel where the computer tells me I have got about 60mpg, I get in reality somewhere between 50 and 55mpg.

I would welcome the opportunity to get this re-calibrated, but would not pay too much to get it fixed - it is not that important.

Exactly my feelings.

Even though mine is just about 4-5% optimistic, not 10%, it's still annoying that such a convenient thing - MPG indication shows data that you should manually recalculate in your mind.

And I don't want to pay to fix something that should be made right from the start. I consider this a (slight) workmanship defect, which we are warranted against.

 

[survey]

Mine is about 10-15% optimistic.

This amount of error makes the computed mpg figure largely useless. The only benefit I get from it is to see if my mpg is going up or down under certain circumstances, eg cold weather, hot weather, effect of speed etc.

But I don't need a computer to tell me this, common sense will do.

On a tank of fuel where the computer tells me I have got about 60mpg, I get in reality somewhere between 50 and 55mpg.

I would welcome the opportunity to get this re-calibrated, but would not pay too much to get it fixed - it is not that important.

10-15% is a large error. I thought my 5-8% was bad enough! As I understand when I have raised this before, the error cannot be corrected by the end user or MB garages. However, like you I would dearly like this matter to be addressed (and not at my cost either!). Maybe a few emails to MB would be useful?

 

[EastExpert]

From my experience with the "Fiver", the skew was always the same, this is why "MPG Correction Factor" worked with such amazing precision.

In fact, it looks like the probes and circuits used to measure consumption, are quite precise by themselves, but just need some initial calibration.

Where do you think we could write about it? Head office of M-B UK?

 

[survey]

From my experience with the "Fiver", the skew was always the same, this is why "MPG Correction Factor" worked with such amazing precision.

In fact, it looks like the probes and circuits used to measure consumption, are quite precise by themselves, but just need some initial calibration.

Where do you think we could write about it? Head office of M-B UK?

Always worth an email to MB Customer Services.

 

[cleverdicky]

Hi Guys just have to interject an observation.

On mine with a similar issue I could never get it to display 'at that moment' mpg. Always average either from start or from reset. So i discovered if you press the trip reset button when moving you can get a spot on mpg. It doesn't reset trip miles either on another screen.

Also if you want to increase your mpg, (on a petrol) clean your spark plugs and check the gaps.

 

[S.Speed]

Hope I am not being pedantic but wouldn't new versus old tyres make a difference as well?

Have to say the onboard mpg indicator on mine is very acurate indeed.
Once did a 360 mile trip to Wales and back and the display was 53.5mpg..
I re brimmend at the original pump and it actually worked out at 52.9mpg.
Thats close enough for me !

 

[djb]

..... So i discovered if you press the trip reset button when moving you can get a spot on mpg. .

I have tried that, mine defaults to 43.7, and then changes from there. My previous 2003 c 200cdi sport defaulted to 50 something if I rememer correctly.

neither default to a instant reading,as Ihave tried a re set rolling down along hill, where it would show 99.9 and going up a long climb, where the fig should be in the low 20s

 

[survey]

Hope I am not being pedantic but wouldn't new versus old tyres make a difference as well?

Have to say the onboard mpg indicator on mine is very acurate indeed.
Once did a 360 mile trip to Wales and back and the display was 53.5mpg..
I re brimmend at the original pump and it actually worked out at 52.9mpg.
Thats close enough for me !

Yes you would think that tyre wear would make a difference. My tyres are getting close to replacement and my trip computer reads optimistically, but I must say has been fairly consistent over the last 15K so maybe tyre wear does not make a difference.

 

[EastExpert]

survey, I agree with you - the difference is consistent from 0 (well, delivery mileage actually) to nearly 7K miles where my car is at now. May be tyre wear is not such a big contributing factor.

cleverdicky, after I press reset, it defaults to 37.6 mpg always (I think it's not so far from the mixed economy figure for my car, by tech sheet.) I am not sure if that's "instant MPG figure" which you see when push OK.

Further, RE: adjustment of MPG, I've sent a message to M-B Customer Service, as you suggested. Received confirmation. Let's see what they have to say.

 

[xavierx]

Interesting that so many people are seeing 5-15% inaccuracy.

In another thread I had posted that I have measured mine brim to brim over 5000 miles using a spreadsheet i have compared the real life fuel use to the cars estimated mpg and found my car to be exactly 0.0mpg out!

I was amazed at this, as like I say this is not a one off tank, this is over 5000 miles (10 tank fills)

If mine can be that good then I have no doubt that others can be adjusted into spec (probably using Star)

A chip tuner once told me that he can re-calliberate the mpg reading to be near perfect on any car.

 

[EastExpert]

...
I have measured mine brim to brim over 5000 miles using a spreadsheet i have compared the real life fuel use to the cars estimated mpg and found my car to be exactly 0.0mpg out!

I was amazed at this, as like I say this is not a one off tank, this is over 5000 miles (10 tank fills)

If mine can be that good then I have no doubt that others can be adjusted into spec (probably using Star)

A chip tuner once told me that he can re-calliberate the mpg reading to be near perfect on any car.

So I think if a chip tuner could do that, sure the Makers must have a solution to this. Mercedes cars are among the most complex cars on the market and definitely not idiots have created them, but very creative people knowing all about cars.

Yes, I also noticed consistency in figures. 4-5% for all 20+ of my brim-to-brims.