A curiousity based question rather than anything please. I've recently aquired a car equipped with a DPF. Can't say I've noticed its presence other than that unlike any previous diesel car I've had it doesn't seem to smoke even briefly under load/high revs. I do use it for regular long trips which I understand suits the DPF process but I was just wondering how I would know if it was functioning properly ? Does the burn cycle manifest itself in any noticeable way ? Also, what are the symptoms of a faulty DPF ? Poor running or mpg or what ?
Just curious as I say, nothing appears to be untoward with mine, just wanted to get the expert advice of the BR in the hope that I never need it....if you see what I mean....
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My DPF smells like a fan heater that has been in the back of a dusty cupboard for a while. I think if they go faulty you get a warning light telling you.
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There are different sorts - something here -
en.wikipedia.org/wiki/Diesel_particulate_filter
AFAIK the Squashy has the fuel-burn type, so now and again will inject some extra fuel late in the cycle to generate extra heat in the DPF and burn the accumulated soot.
When it does this there is an indication - there are some instructions in the book of words, which no doubt you have read from cover to cover ;-)
My work colleague has had a problem with hers though - twice (shortly after a service strangely enough) it has been unable to complete regen and she has had to take it in. They basically said she wasn't driving properly, and issued her with a photocopied instruction sheet that was much more specific than the manual, and said she must drive at no less than 50mph for at least 20 minutes. This is quite difficult in Hemel Hempstead on a weekday tea-time.
If the regen fails, again there is an indication and it presumably goes into limp mode eventually if untreated.
It was when I heard this that I decided never to buy a car with a DPF if there was a sensible alternative - it reminded me of the film "Speed" where the bus will blow up if it drops below 50.
Edited by Manatee on 30/12/2009 at 18:47
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...This is quite difficult in Hemel Hempstead on a weekday tea-time...
Manatee,
Like it, very droll. :)
Usage seems to be the key, though.
I've had no bother with the DPF on the CC3, but it gets some revs every journey, and I regularly do 70/80mph motorway runs of about 30 miles.
I sympathise with drivers who have different usage, not so suited to DPFs.
I'd be hacked off to be told I had to go whizzing around for the sake of it.
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My usage wouldn't suit a DPF equipped car either and i wouldn't really want one, ticking time bomb of a bill there methinks.
I'd spend half me time keeping mental notes and going for pointless thrashes up the road, and still unsure whether it's worked or i've just added to the problem, and the other half measuring the oil level and praying it didn't increase.
Interesting thread on technical where a chap has removed his 206hdi dpf.
I imagine if faulty the dpf will evenually block up and stall the engine if the ecu doesn't shut the car down before that happens.
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I've had a Mondeo IV 2.0 TDCI with DPF for nearly two years and 20K miles. It has no warning light or any sort of indication of the need to regenerate the DPF (unlike VAG, some Vauxhall and Mazda cars).
My observation is that the DPF will 'passively' regenerate on a long run where the engine is revving above 2,000rpm for a length of time. That is, the high exhaust gas temps in these running conditions will get the DPF matrix hot enough to coke the deposits without any help from the ECU.
However, the ECU also seems to order an 'active' regeneration (i.e. by injecting extra fuel, closing a flap in the inlet etc), presumably as a failsafe, every 400 - 500 miles or so. This seems to happen irrespective of the 'cleanliness' of the DPF.
I believe this is the case because on a few occasions, I've noticed a regeneration happening within a day or two AFTER completing long motorway journeys (i.e. 150+ miles in one go, at engine rpms constantly around 2,500rpm in 5th or 6th gear -- in other words, relatively high loadings).
I can tell a regen is happening because a) the throttle response goes a little wooly, b) the engine runs a little lumpily (as if it was a carburated car running stone cold with the choke on) and c) the engine cooling fan comes on, which it never does under any other circumstance.
These 'active' regenerations take 5 minutes, no more. If I'm nearly home and I detect one is happening, a drive round the block for a couple of minutes until the fan goes off is all it takes.
No problems with mine, even though 60% or more of my driving is short hops of less than 5 miles.
Edited to add that the oil level doesn't increase on mine. The one concession I do make to the DPF is that I use third gear in 30 limits which keeps the rpm around 2,000 ... although this is mostly because I find fourth gear is too long in town (30mph = 1250rpm in 4th, I don't like to lug the engine at such low rpm)
Edited by craig-pd130 on 30/12/2009 at 19:34
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OK thanks for the feedback all. Another acronym I hadn't heard of until recently explained.
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I think all DPF`s should be timed to go off at the same time - in a sort of mass exhalation of heat and flame.
Actually, they could be pulsed on and off by radio signals on the Motorway network - in mile long sequences, that could radiate heat signatures, to planets circling other stars - a signal that we are saving our planet - or at least defrosting our roads.
On the Tech front, my Friends car used to purge automatically on being tuned to Terry Wogan - but is now exhibiting signs blockage.
`Umph - can you get in touch?
Edited by oilrag on 31/12/2009 at 08:37
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:-) that's a good idea, Oilrag.
On a semi-serious note, I've seen technical papers which suggest an electrical heating device (in effect, a set of glow plugs fitted within the DPF matrix) can be used to raise the DPF temperature and start coking the soot.
I wonder why manufacturers are not doing this, and instead rely on risky strategies like injecting extra fuel to regenerate DPFs?
The unit cost of a couple of glow plugs and a bit of wiring loom can't be THAT high. Electrical drain shouldn't be a problem as the engine would be running when the glow plugs work. And think how generally reliable glow plugs are in the cylinders.
Edited by craig-pd130 on 31/12/2009 at 09:37
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I wonder why manufacturers are not doing this
Because they will cost more.
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That`s the shear (as in oil shear) beauty of the `squirt derv into the dpf via the piston on exhaust stroke` method.
It costs the manufacturer absolutely nuffink..... just a little tweak on the software.
Got to admire it though. The sophistication of precision control that allows Auntie Nelly to walk safely behind the car without risking becoming a flaming kebab - while Uncle John starts the engine.
The giveaway with these systems is the little drops of derv/engine oil (80/20) that you see on your windscreen in a following vehicle. You just *know* that sooner or later - a 30 yard sheet of flame, burning what was once sump oil, will be ejected from the tail pipe.
All systems `green` then, while Mayon volcano looks on in envy... ;-)
Edited by oilrag on 31/12/2009 at 13:22
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You have mail Oily..
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In the A3 tickover would increase to about 1,000 revs and being a DSG up changes would be made later, as if the car was in sport mode. Nothing more.
On the X type tickover increases, up changes takes longer and on tickover it sounds like the exhaust is blowing.
A3 regenerated about 4 times in two years, X type has done it 5 times in 6 months, last time was about 3 weeks ago during a motorway trip.
Both took about 15-20 miles to go through the process.
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When regenerating, my car has a sweet caramel type smell to the exhaust, the auto box changes up at higher revs and you can definitely notice the fuel consumption increase!
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