Practically Classics Forum

As many will know, diesel engines from about 2008 have had to have diesel particulate filters fitted. For various reasons, some owners don't drive in a manner that lets the filters purge themselves and there has been a good trade in conversions to remove the filters and reprogram the ECU so that it doesn't look for the sensors that say the filter is working.

Having looked at the VWAudi forum, I noticed an interesting thread that says the MOT has changed so that a visual check of the DPF is required (if the car was originally fitted with one) and, if it's missing, it's an MOT fail. I know replacing a broken one is a £1,000+ job at a dealer - but how much will it cost to sort the ECU - can it be simply reprogrammed back to standard settings? I wouldn't blame the dealers if they say no!

http://www.vwaudiforum.co.uk/forum/show ... PF-Removal

There could be some modern diesels with very short MOTs on eBay soon ...

It amuses me somewhat - my Golf has a DPF and I have only had one problem with it - a pressure sensor that put it into limp mode. The sensor was £45 to replace (local garage) - a lot cheaper than a conversion! I don't know about other makes/models, but my (Bluemotion) has a gear indicator that tells you to drop a gear (or go up - occasionally) and it may seem strange having to do 30MPH in 2nd gear, but that's because the DPF is "cleaning" itself! Annoyingly, it does 60 at about 1700RPM in top (5 speed box), so is on the borderline for self purging in normal use. Using the "premium" diesel helps a lot (I use the expensive Shell stuff) and I rarely have to keep the revs up unless I am stuck in traffic.

I think it I mainly city drivers who spend all their time in traffic / low RPM that have problems. There has been a marketing issue with small diesels with DPFs fitted being aimed at city dwellers. Unless you have a 40mph+ blast for a few miles at least once a week they do tend to clog. I have a friend with a Fiat 500 diesel that had to have her DPF replaced firstly under warranty then 2 years later at her own cost. Her problem is the car gets used for a 3 mile drive to the station every day then about 5 miles to tescos once a week. I doubt the car ever gets warm enough for the heater to work let alone to purge the filter. 50mpg is good but not when you build in the cost of a DPF every 2/3 years.

How true Terry. As you know, my current Golf hardly goes anywhere (less than 3K miles a year at the moment), but it rarely goes less than six miles a trip - and most trips are to town (30+ mile round trip), so it gets properly hot - and will often purge on the way home when I can get a bit of speed up!

I think it was about three years ago when I saw Anne Robinson on Watchdog having a go at manufacturers about fitting DPFs that "kept failing" on cars! Of course, in usual journalist-fashion, she blamed the manufacturers rather than the car owners! I suppose that telling viewers that they only had themselves to blame if they weren't reading the owner's manual - or not following the instructions therein - wasn't good TV!

The DPF on the Smart was a proper awkward little bast4rd, it would always decide to regenerate the moment I pulled the car onto the drive after a run! But sitting with the engine idling and watching for the idle speed dropping back from 1100rpm to the correct 700rpm became routine and the DPF was one of the few bits of the car that wasn't dead at two years and 40,000ish miles.

The Golf, on the other hand, has only made its presence known once since I bought the car, that time I was sitting at some roadworks - on the way through Lauder - where lights both ends were red and a digger had fallen into the trench between so nobody was going anywhere. In these circumstances, I'd normally press the brake hard enough to turn the engine off (a gentler stab simply applies the parking brake) and sit waiting without using Diesel but on that occasion, the idle was up from 800 to 1000 and the oil was up from 93 to 98 degrees so the inevitable happened and it did a Dr Who job on itself. Three minutes later, and three seconds before the traffic was moving again, the idle dropped to normal and off we went. But it all happens seamlessly and there's never been a time in either car when I've been aware of regen taking place during normal driving, no doubt helped by the VW's oil stat being operated by electronic witchcraft so that it can get hot enough to do the job without interrupting my progress.
Mine does 1600rpm at 70 in 7th but it only ever changes down to 6th on long runs if I switch from "eco" to normal or Sport mode in settings on the dash, there's no point as all that does is makes the engine audible.
Remarkably, for a short stroke, 16 valve engine it's still like the older, 1.9PD engines by being quickest by using a setting that changes up at lower engine speeds and as long as the oil gets warm enough, then it regenerates without spoiling my day. Now at a shade under 7,000 miles, the display tells me that it's only regenerated half a dozen times in total since it was new so why the likes of VAG refuse to sell Diesels to IoW's residents and those on Lewis and similarly small Islands is a mystery to me as the current Diesels will regenerate when they need to do so, even if it means the engine runs on for the required two or three minutes after the journey has ended.
The DPF uses typically only 15ml of Diesel to set it away, plus the extra it uses because of the faster idle. Overall, it still uses roughly 18% less fuel than Dad's '07 plate Mexican Jetta with 1.9PD engine and only 6 forward gears in its heavier "wet" DSG and the Jetta's not a thirsty thing by any means. Thank Goodness I don't stay on a tiny Island though, or they wouldn't have been allowed to sell a Diesel to me.

Definitely a problem with the owners (and bloody Watchdog), not with the technology itself which seems to work well enough. People who switch off when a regen is happening only have themselves to blame if their filter goes wrong. This same mentality is why some folk, mostly in California, drive head on into something hard and heavy then sue the maker of their pickup, RV or SUV because they chipped a toenail and the handbook didn't warn against this!

As far as the MOT test goes, surely the clouds of black smoke would tell any tester with working eyes that the car being presented had had its DPF removed?

I will have to investigate and see how to tell how many times mine has regenerated :S It was an optional extra fitted by Travis Perkins to mine when it was new. If it were to go wrong I would just remove it as I have the software to re-program the various ECUs. I'm sure that the solution to all DPF problems is to put your foot down more often
I am booked in on Saturday morning for 4 new tyres so I have was driving even more enthusiastically this morning to make the most of the outgoing ones

TerryG wrote:I'm sure that the solution to all DPF problems is to put your foot down more often

Do that by all means, but find a different excuse for doing it** because the idea that the engine needs to be thrashed to regenerate the filter is a big hairy old myth! As long as the engine is at operating temperature, then a filter is just as likely to regenerate at idle in a town as it is on a motorway at the legal limit. I believe that there are many more uninformed or badly informed owners than there are bad bits of technology. Imagine how many people ran up the back of those cars which had newfangled four wheel brakes back in the 1920s. Dreadful idea that, fitting brakes to the front as well! Just as well it never caught on or we'd all be causing collisions by our use of modern technology.

**- Top excuse for ragging the arse off a car in this Month's official "Reason for ragging the arse off a car" chart is:
"It has a slightly sticky caliper piston but by driving like an eleven year old from Middlesbrough, it does ease off a little; hence my exuberant driving style, Officer."

"Oh I see, sorry to have inconvenienced you Sir, you have a nice day now!"

I'm thankful the modern didn't get a DPF fitted, it was at a time it was pot luck if it got one or not, however it still needs a good blat to clear things out now and again, as it will soot up the variable turbo vanes etc if left too long, but it's been 100% better since I blocked the EGR valve off, now those are the biggest con and swizz going IMO

I was getting an EGR warning until I (quite literally) bashed it with a rubber hammer in frustration. fault cleared. It is amazing how often I apply my rubber hammer to malfunctioning car parts and it either makes a satisfying (and often expensive) crunch or fixes the problem.
With some configurations (including mine) blocking off the EGR will result in lean running without some ECU fiddling.

What is it with you and hammers Terry? First computers and now cars!

When I was an agricultural student (so many years ago ), a joiner was watching the boss repair a fence and said something like "Farmers, they aren't brickies, they aren't joiners but by F*** they can bang in nails"!

if you listen to radio 4 tomorrow its all about diesels... john i expect to hear you on the programme
http://www.bbc.co.uk/programmes/b006qps ... s/upcoming