Intermittent Poor Fuel Consumption

BillyBoy

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OK, so E400d, 5 months old, OM656 engine. So far, I've been very impressed with the fuel economy from the car, especially as it's permanent 4WD, and goes like excrement off a shovel! I have one issue, however and wonder if anyone has any insights.

I have had 5 occasions where I have had really poor fuel economy from the car. The ones on the way to work are easiest to quantify. My readout for commuting 33 miles to work is pretty consistent - typically 41.5 - 42.8, however on odd occasions, I really struggle to get over 30. This happened yesterday and has happened a couple of times before. Call me sad if you want, but I have several "checkpoints" on my journey where I know what the MPG should be reading. One of these at the end of a long stretch of dual carriageway is just over 40 MPG, however yesterday is was 24 MPG (40% down) at the same point. The economy seems to improve again after a while, and by the time I got to work it was up to 30.7 MPG (approx 25% down). Driving home was back to normal economy.

When the car is having a "funny", even feathering the throttle lightly on the flat causes the instantaneous economy to drop dramatically (sub 10 MPG), but after a period it is back to more normal behaviour. My first thought is the car is doing a DPF Regen and throwing in extra fuel, but 5 DPF Regens in 4,500 miles? Seems way too often. The car is used for quite a lot of long journeys, with some tatting about in town as well.

Will be taking it into MB as it's obviously still under warranty, but wondered if anyone had any ideas?

TIA :)
 
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BillyBoy

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Hmm - thanks for the link. Given that I do mostly 33 mile each way commutes in the car, it should be doing passive regen really, not active. I never noticed this behaviour on the 220d. Will speak with the garage and see if there is anything causing unnecessary active regen (or if it's actually nothing related to the DPF and a fault on an injector or something!)
 

malcolm E53 AMG

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Don’t rule out a sticking thermostat, mine started sticking on my OM642 with a mpg drop of 30% eventually failing in the open position, the mpg was horrendous circa 20mpg even on a good run

Regarding the DPF, 4/5 regenerations in 4.5k miles is very good my OM642 with the type of motoring I do would regen every 400 miles so double yours
 

M80

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2014 639 Viano- 651, 5sp Auto. 2009 S211- 646, 5sp Auto.
I'm with the rest and guessing DPF incineration.
My 651 will reincinerate at approx 540 miles while running longer motorway journeys.
On less distance runs it dropped to some where above 400miles.

I can only guess at the comparable consumption during the incineration but it looks to me to be around half for up to 10 miles (as low as 6 miles). Easy calc suggests that the consumption might be around 2% better without the DPF.

I would keep an eye on the fill to fill calculated consumption and see what that tells you.
Checking the stat for getting up to temp and holding it is worthwhile.
Your consumption increases this time of year anyway, colder start, slower warm up and winter additives.

Is the increased distances between incinerations due to the adblue?
 

John Laidlaw

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Sounds like the passive regen isn't happening for some reason (it should be given your driving profile) and active is happening.
My current car is doing a 15 mile each way commute largely motorway and in the 6 weeks or so I've had it, it has done 1 x active regen (revs were up, fan running hard), it was interrupted but resumed when I next started up. This is borderline and a day a week I extend one of the journeys by 10 minutes to make sure I give the passive enough time to do it's job 20 minutes + is the recommendation.
I have just bought Bimmerlink and the necessary cables so I can monitor the regen activity log and soot content in the DPF.
I had an 'Oil overfilled' incident a few days into owning the car and suspect the previous owner didn't use the car on 50mph + journeys much (had the same myself on the XC90 as the wife was hardly driving it anywhere, which is one of the reasons it's going at the end of this month).
I don't think the AdBlue will have any effect the distance on incinerations as that's to reduce NOX , the DPF is capturing the soot, it's the raw fuel being dumped in to create an active regen which causes extra fuel consumption. What doesn't help is if that regen doesn't complete often enough the diesel must go somewhere and somewhere is in the sump....that's not ideal.
Nothing simple about owning and driving a modern diesel, that's for sure....
 

ajlsl600

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There are a number of side effects to owning a modern diesel near all of which are NOT explained to buyers. And therein is where most problems originate
A dpf light on dash,continue for 20 min might have helped.or a picture of handbook on light
Along with ,on windscreen in showroom...this car cant tow anything in its std guise . .there are others but these would be a good start.
 

malcolm E53 AMG

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Sounds like the passive regen isn't happening for some reason (it should be given your driving profile) and active is happening.
My current car is doing a 15 mile each way commute largely motorway and in the 6 weeks or so I've had it, it has done 1 x active regen (revs were up, fan running hard), it was interrupted but resumed when I next started up. This is borderline and a day a week I extend one of the journeys by 10 minutes to make sure I give the passive enough time to do it's job 20 minutes + is the recommendation.
I have just bought Bimmerlink and the necessary cables so I can monitor the regen activity log and soot content in the DPF.
I had an 'Oil overfilled' incident a few days into owning the car and suspect the previous owner didn't use the car on 50mph + journeys much (had the same myself on the XC90 as the wife was hardly driving it anywhere, which is one of the reasons it's going at the end of this month).
I don't think the AdBlue will have any effect the distance on incinerations as that's to reduce NOX , the DPF is capturing the soot, it's the raw fuel being dumped in to create an active regen which causes extra fuel consumption. What doesn't help is if that regen doesn't complete often enough the diesel must go somewhere and somewhere is in the sump....that's not ideal.
Nothing simple about owning and driving a modern diesel, that's for sure....

Yes I always try where possible to make sure the regeneration completes once commenced can be a bit of a pain but worth doing in my opinion (wife thinks I’m mad of course but doesn’t say anything lol)
 

ajlsl600

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Yes I always try where possible to make sure the regeneration completes once commenced can be a bit of a pain but worth doing in my opinion (wife thinks I’m mad of course but
doesn’t say anything lol)
And thats why makers,in my case benz dont advise anyone! cos in days where mpg is king ,how are they going to sell something NOT suited to short runs or where drivers need to drive around aimlessly burning fuel at 15mpg to save the planet, no one would buy them !
 

John Laidlaw

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And thats why makers,in my case benz dont advise anyone! cos in days where mpg is king ,how are they going to sell something NOT suited to short runs or where drivers need to drive around aimlessly burning fuel at 15mpg to save the planet, no one would buy them !
So true. Many car manufacturers (not just MB)have singularly ignored (and in fact deliberately hid) the fact that emissions and technology designed to reduce consumption of diesel and it's pollution , due to their determination to sell more units at any cost, even if the customers in a huge number of cases in no way benefitted from, nor had the profile to use, Diesel technology correctly.
Volvo leased us an XC90 diesel on a 6k/year lease! How were there no warning signals there?
I notice on the (less than) small print now on lease company web sites they have a large disclaimer, and subsequent advice on driving profile vs Diesel and DPF damage.
 

malcolm E53 AMG

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And thats why makers,in my case benz dont advise anyone! cos in days where mpg is king ,how are they going to sell something NOT suited to short runs or where drivers need to drive around aimlessly burning fuel at 15mpg to save the planet, no one would buy them !

Just my way of dealing with the DPF issue, environmentally we can categorise it with speed humps from a fuel burning point of view - incidentally the local council have started to remove some of local speed reducing measures which is interesting certainly makes for more enjoyable driving - whatever next!
 

John Laidlaw

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Just my way of dealing with the DPF issue, environmentally we can categorise it with speed humps from a fuel burning point of view - incidentally the local council have started to remove some of local speed reducing measures which is interesting certainly makes for more enjoyable driving - whatever next!
True Malcolm, only issue I have is additional miles and time falsely added to journeys just to avoid 'mechanical' issues. Bit counter intuitive. This is exacerbated by our current situation when there is no where to drive to! On the Wirral here we're a bit stuck as we're discouraged from crossing into Cheshire currently and completely forbidden from entering Wales....
 

James E400D

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Sounds exactly the same as my E400D.... Wonderful thing but she has a particularly aggressive DPF regen!

In my experience the car will hold onto gears until 2k revs or more, high idle, average 21mpg or so on journeys that I usually get mid 40s on...

I've owned various diesel BMW's and Audi's with DPFs over the years and never experienced that kind of drop in fuel economy, or such obvious regen behaviour. Such a shame for what is otherwise a stunning powertrain!

Did you get anywhere with the dealer? Poole Mercedes-Benz never called me back after raising the issue with them....
 
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BillyBoy

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The supplying dealer is by work, and we are locked out the office until December so will pick it up with them then. I have another issue with the drivers assistance pack so am collating data / evidence to present to them when I take it in. It's good (or bad) to know mine is not an isolated case as at least it means there may be a fix at some point.
 

James E400D

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Any update from your dealer on the DPF regen issues? Still experiencing the same symptoms with mine despite using only BP Ultimate diesel and long runs
 
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BillyBoy

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Not been in yet as a result of lockdowns and tier three, I'm not travelling. Interesting you say that, it was something I had considered - my 220d was primarily run on Sainsbury's diesel, however I have been using Shell Ultimate (or whatever it's called) in the 400d. I have been wondering whether to switch to Sainsbury's and see if I still get the same issue. Can't really see why the OM654 should be so different to the OM656.
 

mattkh

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..... - incidentally the local council have started to remove some of local speed reducing measures which is interesting certainly makes for more enjoyable driving - whatever next!
Next....20mph on roads.
 

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