w204 C220 om 651 2012 terrible fuel consumption...

[felloffajetski27]

Hello all

New poster here but have been lurking for a long time,

My C220 is a well maintained car from new, I am 2nd owner. Serviced often by myself. Only issues I have had have been DPF related , I have had to change the differential pressure switch once. I have also had a timing chain and tensioner replaced. Milaege now on 196k

Car happily achieved decent MPG in the past. A while back though the car went in for an airbag recall and I asked them not to do the emissions software update, but predictably they did it anyhow, and since then this is where I have noticed a large decrease in fuel economy.

I am wondering though is it just down to this software update, or do I have another issue. I have icarsoft mb2.0 diagnostics so have been looking for clues and the only issue i see is the Y85 EGR cooler bypass switchover valve fault 53336/6058. The care drives fine, plenty of power, no other faults. I have looked at diagnostics on load and full acceleration , car pulls well no faults, boost pressure around 2.7bar etc

I have noticed DPf seems to fill to 100% fairly quickly , say 1% every mile or so which seems high.....could this DPF regen looping often be causing worse economy? I uderstand it uses fuel to regen so this is plausible.

Could the fact the DPF is on 196k and presumably the same from new be an issue?? Ive tried running injector fuel additive etc without much success.

As I say car performs normally, temperature gets up quickly and sits at 90 as it should, no leaks, car drives beautifully apart from the awful MPG - im getting circa 400 to 450 miles to a full tank. Calculated properly fuel consumption around 37mpg over a full tank. Tyre pressures fine, no dragging brakes etc.

I wonder if the Y85 is causing issues, or is it just the fact I have had the emission update and that is the soul cause??
Please help!

Thanks
Paul

 

[Jonesy161]

Sorry, can’t help with the diagnostics, but, if you do a search on here or generally you will find many fuel consumption issues relating to the software update.
I also remember one of the members explaining why this happens.
Good luck

 

[Stratman]

What temperature does the engine run at? Does it get to 90 degrees within around five minutes or so and stay there in town and on the motorway? If not the thermostat is faulty and this will cause higher fuel consumption. It won't be the sole contributor, the software update is famous for ruining it too.

 

[felloffajetski27]

What temperature does the engine run at? Does it get to 90 degrees within around five minutes or so and stay there in town and on the motorway? If not the thermostat is faulty and this will cause higher fuel consumption. It won't be the sole contributor, the software update is famous for ruining it too.

hello, yes it gets upto temp fine and sits at 90 or just over

 

[markjay]

If you say that the poor fuel consumption issue started after the Dieselgate software update... then looking for other reasons may prove to be a wild goose chase.

Also, does your car have automatic transmission? My understanding is that part of what the update does is causing the transmission to shift gears at higher engine revs than it did before, which can explain the poor fuel economy. Does the car go into top gear (7th) when cruising at 70mph?

 

[geoffus]

Is it using more fuel as indicating on the display or brim to brim ?
Or is it now reading correctly after the update ?
I recently drove up to the Lake District and the display read average 59 mpg over 200 odd miles, on return trip I brimmed the tank and checked when I got home, mpg was around actual 45 mpg or thereabouts, so way out.
2012 B200.

 

[markjay]

Is it using more fuel as indicating on the display or brim to brim ?
Or is it now reading correctly after the update ?
I recently drove up to the Lake District and the display read average 59 mpg over 200 odd miles, on return trip I brimmed the tank and checked when I got home, mpg was around actual 45 mpg or thereabouts, so way out.
2012 B200.

I don't know how accurate the onboard computer's mpg calculation is, but equally I am not convinced that it has been proven that 'brim-to-brim' is accurate, either.

Was is the filing station and the same pump? Was the nozzle inserted in the same way, and allowed to pop at the same time? Arguably the ambient temperature can make a difference, too.

To clarify, I am not suggesting that I know for fact which of the two methods - onboard computer or brim-to-brim - is more reliable, just that I don't understand why people assume that brim-to-brim is an accurate measure.

EDIT: will Google to see if anyone carried out an experiment to try and establish it...

 

[Stratman]

Both onboard computer and brim-to-brim rely on the car's odometer for the mileage reading, so the question really is which meters fuel more accurately, the pump or the car's fuel system?

 

[markjay]

Both onboard computer and brim-to-brim rely on the car's odometer for the mileage reading, so the question really is which meters fuel more accurately, the pump or the car's fuel system?

You could argue that if both use the same odometer, then this won't affect the discrepancy (because the accuracy or inaccuracy in the mileage reading will be the same).

As for "meters fuel more accurately", yes, but it's not the only parameter - the pump may be accurate, but the method of determining when a tank is brimmed, might not be.

 

[Tonygw]

It does sound likely that the software downgrade has caused the issue. I have heard many similar cases of poor running and terrible mpg after the software downgrade. When mine went in for the airbag recall I had to tell the customer service agent and emailed them to confirm that I did not want any changes to the software. They confirmed this was fine.
When I dropped the car off I doubled checked that they would not perform any software changes, they strangely had no record of me refusing the software change but said it was fine to refuse. I made them state on the service sheet that no software change was to be made. I also taped over the OBD port with a note saying do not touch..

I am pretty confident they didn't change anything. And only did the airbag recall.

At 196K the dpf may well be pretty full and may need to be removed and cleaned, they do clog up eventually.

My car is a C250 but same engine, I usually get about 450miles to a full tank but I do tend to drive spiritedly and not with economy in mind.

If the gearbox is holding on to the gears for longer after the software change, a gearbox reset may help and is easy to do. May have an effect, might not. (google gearbox reset w204)

good luck

 

[felloffajetski27]

hello all

no the transmission is the same as before, i still still get 7th gear fine on motorway etc

i have calculated mpg from brim to brim and using the cars own mpg calcs.

yea i think perhaps the DPF is full, altho diagnostics only says 2grams of ash and 1 gram of soot

 

[geoffus]

So you are saying the brim to brim and cars computer are reading MPG the same ?
Mines way out.

 

[felloffajetski27]

So you are saying the brim to brim and cars computer are reading MPG the same ?
Mines way out.

no mate they are not the same

brim to brim using milaege and fuel reciept etc so can work accurately is the best. i do this all the time

 

[geoffus]

no mate they are not the same

brim to brim using milaege and fuel reciept etc so can work accurately is the best. i do this all the time

What MPG did you get before the update ?
Was the previous MPG measured using brim to brim and how far out is your dashboard compared to this ?

 

[markjay]

hello all

no the transmission is the same as before, i still still get 7th gear fine on motorway etc...

Yes it will do that but the question is at what speed.... does it go into 7th gear at 70mph?

 

[felloffajetski27]

Yes it will do that but the question is at what speed.... does it go into 7th gear at 70mph?

yes like normal