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Discussion Starter #1 (Edited)
Hi guys,

I have a 2007 159 and after months of trouble, chugging, coughing, sluggishness (you get the picture) etc...and one expensive breakdown later... I had my EGR blanked after it had stuck open from carbon build up and the swirl flaps removed after becoming heavily clogged from this, and had the system cleaned up real nice.
The car is an absolute dream now, and has continued to be....

Except....I have noticed something rather frustrating going on inconsistently with my MPGs/fuel consumption and wondered if anyone can give me some technical advice into what on earth is going on as its costing me a lot when it happens...

So, firstly, before I start I have manually measured my MPGs. I've done this 4 times and it is spot on to my Trip A Average MPG reading.

So, the issue I've noticed is every so many miles my MPGs drop to around 30, and no matter how I drive it won't go up. I can't figure out if its every 70, 100, 150, or 500 miles but it happens whenever it feels like it - its not consistent.

It lasts for a good 30-50 miles or so before going back to normal.

So, whilst driving at 60, around 1800 rpms, my current MPGS don't go higher than 35. This was on a flat. Uphill or in traffic its as low as 7-17mpg on average.
If i take my foot off the accelerator it takes ages to go up to 99.9 - i usually have to put my foot on the accelerator again before it gets there.

Then when its fine again, still driving at 60, and around 1800 rpms, its back up to 50-75 current mpgs on flats, and i've even measure 58.1 going up hill!!
So what's going on when its dropping because I've used a return journeys worth of fuel in a single journey.

Does anyone know what on earth is going on? Is it normal for EGR blanking because it doesn't seem right to me?

And i thought my fuel consumption should be better by 12%....which it is when it's fine, but then the drop is making up for that!! :(

As i said above, aside from that, i've not noticed any sluggishness. It's been a dream to drive, but I can practically see my fuel gage move as if I had a V6 again...just without the V6 engine! Haha!... :eek:

I drive 25 miles to and from work. This usally takes me 25-35 mins and on a good day my Average MPGs are 51-54.
And when its bad my average is 28-32 :-( so almost double the fuel!!

Any comments appreciated.
Thank you :)
Bev
 

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Does the exhaust note sound boomier? It could well be the DPF regenerating...

Other ways to test is if you take your foot off the accelerator and coast, the current consumption will go from 99.9mpg down to about 30 then blip back up to 99.9 again.

Or look at your boost gauge, does it drop to zero sharply the minute you take your foot off the power?

Sorry if i'm teaching you to suck eggs, but it sounds pretty much like the engines going into a DPF regen more often than it should.
 

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Does sound like your car is regenin to much. It should happen every 16 to 20 hours of running. How many miles have you got and is it on the original dpf. ? A standard regent takes about 10 mins. Is that how long your car shows low mpg ?
If its blocked the car willl keep regenerate ing , have you got access to Any software for the car. Fes or mes
That's when it uses more dieselto burn off in the exhaust stroke to heat up the dpf to 600 c to burn out the soot.
 

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Discussion Starter #4
Hi guys, thank you for your comments.

I've just edited - basically when I take my foot off the accelerator it creeps up, but I usually have to accelerate before it even reaches 99.9. Whereas on a good day it takes seconds to get to 99.9+ as you probably know.

I drive 25 miles to and from work. This usually takes me 25-35 mins - and on a good day my Average MPGs are 51-54.
And when its bad my average is 28-32 :-( So almost double the fuel!!

BTW - does a regen give off a burning rubber smell from the rear of the car.....??.....
 

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BTW - does a regen give off a burning rubber smell from the rear of the car.....??..... yes, that is a regen plus mpg drops to 10-15 mpg on mine
 

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yup your regenerating the dpf :)

However i'd recommend not de-dpf'ing the car as the eu are about to make it illegal/an mot failure if a car that doesn't have a dpf that came with one from the factory...

use FES or MES to do a regen, and that should sort it out, but i do similar mileage and journies to you, and once a week without fail it will do one on a long stretch of road on the way to work...so annoying, avg mpg before is 42, after it's 33...you're basically setting fire to £ notes.
 
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