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+--- Thread: DPF ? The reason for poor economy? (/Thread-DPF-The-reason-for-poor-economy)
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DPF ? The reason for poor economy? - ED209 - 09-04-2012 08:20pm
The below refers to a volvo but as our cars will have DPF could it be the same reason most are struggling to get anywhere near claimed economy figures?
http://www.telegraph.co.uk/motoring/caradvice/honestjohn/9188483/Trouble-matching-claimed-economy.html
RE: DPF ? The reason for poor economy? - ytshome - 09-04-2012 11:02pm
Wouldn't surprise me Ed. mostly short trips I'm still just under 28 mpg.
RE: DPF ? The reason for poor economy? - ED209 - 09-04-2012 11:11pm
Been reading up a bit and yes it looks like the engine burns more fuel in order to in crease exhaust temp and regenerate the dpf so fuel consumption is increased. First sign of an issue mine is getting replaced with a piece of stainless steel.
RE: DPF ? The reason for poor economy? - PhilSkill - 09-04-2012 11:21pm
Certainly not going to help mpg using fuel to regenerate and needing to drive the car with higher revs to do it, also DPF is another thing in the exhaust flow restricting the Engine so less mpg again. Another EU foolish decision in the misconception of what constitutes green values for planet earth, using up rare earth minerals to remove some soot from exhausts and waste further oil doing it.
One would hope the DPF was fitted in the official mpg tests...?
Note the official tests are also done without any ancilliaries like Air con, heaters, audio etc on
RE: DPF ? The reason for poor economy? - mickydd - 09-04-2012 11:22pm
Ed, This looks like it could well be the reason for the poor mpg.
See below copy of actual mpg for Evoque against manufacturers declared mpg.
There is as we all know, a substantial difference.
Enter your own real world mpg here:
http://www.honestjohn.co.uk/RealMpg/Results?manufacturer=land-rover
RE: DPF ? The reason for poor economy? - J77 - 10-04-2012 12:38am
I don't have a problem with fuel economy regularly hit 42mpg and have had it at 48.9 mpg not what LR claim but I wasn't expecting it to. At the moment just on short journeys it's about 35mpg.
Does it burn extra fuel? That depends whether it is a passive DPF or an active DPF. On active DPFs the
ECU makes changes to the fuel injectors to allow the regeneration process to take place. Passive DPFs are cleaned by long drives allowing the exhaust to reach a high enough temperature to start the regeneration process. According to the owners manual it should take about 10-20mins at speeds between 40-70mph to regenerate, so I would assume it is a passive DPF.
The above is just how I interpret the information I have read I am no mechanic so please don't shoot me down in flames if it is wrong.
RE: DPF ? The reason for poor economy? - RacingSnake - 10-04-2012 07:23am
But the DPF also causes a whopping great restriction in the exhaust flow.
It is pretty well known that DPF's severly reduce economy, which is why there are kits to enable you to remove them and bolt them back for the MOT.
I was chatting to a tuning friend of mine and he said that in the 'VW' world someone has developed a switchable DBF (and CAT) bypass system.
It does however make me wonder about the comment up there ^^^ as to whether they were fitted to the economy tests run by LR... after all, would the pre-production cars need to adhere to type approval? I assume not?
RE: DPF ? The reason for poor economy? - XFullFatTim - 10-04-2012 09:24am
I think you are all missing a point here guys...................... we are all whinging that the Evoque in diesel engined form is not meeting it's official claimed figures - the fact that there is a DPF there is of no consequence because for the official tests the car must have had a DPF fitted. A DPF will have had to be fitted to the test car to gain homologation/ type approval as construction rules require one.
RE: DPF ? The reason for poor economy? - ED209 - 10-04-2012 09:27am
(10-04-2012 09:24am)XFullFatTim Wrote: I think you are all missing a point here guys...................... we are all whinging that the Evoque in diesel engined form is not meeting it's official claimed figures - the fact that there is a DPF there is of no consequence because for the official tests the car must have had a DPF fitted. A DPF will have had to be fitted to the test car to gain homologation/ type approval as construction rules require one.
According to the initial post, DPF's are not included in the EU lab tests the figures come from.
RE: DPF ? The reason for poor economy? - Donny Dog - 10-04-2012 09:40am
(09-04-2012 11:11pm)ED209 Wrote: Been reading up a bit and yes it looks like the engine burns more fuel in order to in crease exhaust temp and regenerate the dpf so fuel consumption is increased. First sign of an issue mine is getting replaced with a piece of stainless steel.
The engine will probably need re-mapping, though, to cater for the changed resistance in the exhaust, etc.
(10-04-2012 07:23am)RacingSnake Wrote: which is why there are kits to enable you to remove them and bolt them back for the MOT.
It's not actually a requirement of the MOT, only for the type approval. It's a bit like the daylight running lights in that respect - you have to have them fitted, but you don't have to use them. (But the kit will need to alter the engine management to account for their removal).
(10-04-2012 09:27am)ED209 Wrote: According to the initial post, DPF's are not included in the EU lab tests the figures come from.
If you think about it, if the regeneration process is only occasional, the test wouldn't have lasted long enough for this to happen. (The resistance, of course, would still be there, if it were fitted for the test, but I don't know what the relative effects are between the extra 'burn' and the extra exhaust resistance).