[Closed] New MOT rules on DPF removal

Wonder if that means Ill stop getting an advisory for having a plastic under tray every year as they will have to remove it to look.

The documents linked from that page aren't clear on whether you will fail if its just missing or fail if they test the exhaust and it has particulates in it that should be trapped by the DPF. Maybe Ill hold off removing mine a little longer!

Mine has a decat and I understand should fail, but it passes the emissions tests and the tester will only spot it if he knows exactly where to look, what he's looking for, and most importantly can be bothered. I suspect this falls under the same umbrella. As long as it's physically there, how will he know it's hollow?

The actual wording's weak isn't it... Do you have a filter, just modified, or is it modified to the extent that it's not a filter?

I have a filter, but it was a drilled through. It would pass a visula check. Emissions tests on diesels are just a smoke opacity test as far as I know and it doesn't sound like that is changing, but the doc is so woolly who knows?

I *think* the opacity test was tightened a couple of years back for cars built after 2008 but again is still pretty liberal.

Whatever happens I'm going back to a naturally aspirated petrol car, most of my mileage is expensed so trading in economy for reliability sounds like a good move.

If the test is going to be really tight I am tempted to get an MOT done before the end of the month and then run the car for a year or breaks. Once its 11 years old it won't be worth much so selling for scrap or low trade in won't bother me too much.

If the dpf is still there and hollowed out then you won't have any problems as it's only a visual check.

Hi PePPeR,

Is that a fact backed by documentation, I've not seen anything yet? My MOT runs out in April so happy to MOT now rather than risk having a car that won't pass without £600+ spending on it.

Cheers

I find it quite weird that you guys seem happy for everyone to suck up the shit that's coming out of the back of your oil burners, you are supposedly cyclists I'd have thought pollution would at least figure somewhere on your radar.

Joolsburger, a DPF does not magically get rid of the particles it filters, the cars software just chooses a time that it sees fit to do so, & in one big lump, so I don't know if that changes your view of the matter or is of any help?

However just about the only place you'll get a DPF to regen is on a motorway or long dual carriageway, not really places you'll find peds or cyclists to breath in the crap.

I find it quite weird that you guys seem happy for everyone to suck up the shit that's coming out of the back of your oil burners,

That took seven posts. The hand wringers are getting slack around here.

https://www.gov.uk/government/news/new-rules-for-mot-to-test-for-diesel-particulate-filter

The MOT tester will get notification that your vehicle should have one the vehicle when they print the test sheet out.

The tester will have to visually check its still there but that's all they can do. If you have a filter thats been knocked out there's no way of being able to check inside it.

Me, I made damm sure I bought my wifes last car without one on it!

2unfit2ride is right the car still dumps the particles but at the time it chooses to do so.

I think it is and can only be a visual check as IIRC the MOT does not allow for any check that requires anything to be dismantled and reassembled. For the same reason I would be very surprised if anyone failed for running 100W headlight bulbs. Yeah, headlight function and alignment will be checked, but the actual bulb will not be taken out and examined.

The point I was making was you still get the same amount of soot in the atmosphere, but yes I see cyclists on main roads where cars could regen.

Wonder if that means Ill stop getting an advisory for having a plastic under tray every year as they will have to remove it to look.

They can't remove/change anything, one wouldn't even fold the back seat up in mine to test the seatbelts, just noted it as an advisory that seatbelts weren't available to be tested. Although IIRC they can refuse to test it or fail it if they believe you're hiding something. So an aftermarket undertray appearing where the DPF or CAT used to be might not pass.

That took seven posts. The hand wringers are getting slack around here.

I was thinking the same but bit my tongue, it is horrible cycling behind some diesels though in traffic.

"Hand wringers" is a bit of a poor effort IMO. You really need to throw in a "tree hugger", a "yoghurt knitter" and maybe even a good old-fashioned "lentil-muncher" to really get those gobbets of spittle flying.

Joolsburger, a DPF does not magically get rid of the particles it filters, the cars software just chooses a time that it sees fit to do so, & in one big lump

Wrong. It burns it off, into CO2. Collecting the actual soot to be released later would be next to impossible. Were you imagining a little door opening and a tiny housekeeper shaking out the filter as you drive along?

However just about the only place you'll get a DPF to regen is on a motorway or long dual carriageway

Not really. The exhaust gas just has to be hot enough. Normally this would mean motorway but the engine has special ways of increasing the exhaust temperature artificially. It just needs enough time.

Does it not just burn off albeit at a higher temperature?
I have regened lots of diesels and you defiantly get a big cloud of soot, but I may of missed the lump of carbon dropping on the floor 😉

Hand wringer? Not really, just someone who actually cycles and every so often sucks in a nice big mouthful of black smoke from some under maintained deisel shitbox.

Does it not just burn off albeit at a higher temperature?
I have regened lots of diesels and you defiantly get a big cloud of soot, bit I may of missed the lump of carbon dropping on the floor.

Not meant to, it saves up the deposits until they can be burned. I.e. consumed by combustion at a decent temperature, not just flushed out. IT would normally happen on the fly and in a continuing process but those who use their car start-stop a lot find the capacity of the DPF is limited and need to force a flush.

There's always a trade-off anyway, those facing amassive bill could scrap their old car and go buy a newly produced, newly carbon-financed machine that runs a bit cleaner but just cost christ knows how much pollution to build, it just happens to be away from the tailpipe.

At the end of the day the general filtration of new tech into the market is going to happen no matter what, it makes little sense to police the few older cars that don't get scrapped and are kept alive by mildly dodgy means IMO.

[quote=joolsburger ]Hand wringer? Not really, just someone who actually cycles and every so often sucks in a nice big mouthful of black smoke from some under maintained deisel shitbox.

Though you don't have to have a DPF to have a well maintained diesel which doesn't emit clouds of noxious soot.

I agree with molgrips - a DPF doesn't emit the soot, it burns it off. My understanding is that motorway/DC isn't required either - supposedly the threshold speed is ~40mph, and personally I get over that every time I drive.

Just think of all that green fail, when people scrap 5yr old cars to buy new ones , as the DPF repair is more than the cars value. All those cars being dismantled and nasty chemicals and oils etc. Great idea to get rid of pollutants, not, but the only real way is to not drive. I am sitting on the fence on removing my DPF , as forgot to ask my MOT man last month about it. The idea of a diesel is slow revving low consumption, but when you have to run at higher speeds for dpf cleaning, sort of wastes the diesel theory, as it injects neat diesel and eoloys to complete the cycle. Might just get a V8 petrol next to join the 24 mpg focus ST I have. 😉

If you're doing sustained 40+ speeds, I seem to remember about 10-15 minutes is needed, so you're almost certainly going to be on a DC or a motorway.

It's not the soot you can see that is the issue, the really bad stuff is invisible. That's the stuff the DPF is there to filter out. And it's an inevitable side effect of a diesel, it's not caused by poor maintanence.

Would you really scrap a £5,000 car for the sake of a £700 repair? Do you get rid of cars when their tyres wear out? Anyway when drivers and mechanics stop being so dense the bills will become much rarer. DPF blocked? Replace it, oh look it's blocked again. Of course it is. Why is your engine producing more soot than normal and why is regen not working?

visual dpf check, and existing smoke test.
particulate testing is far too expensive and requires specific drive cycle under load which is not practical for uk mot.

dpf actually makes more health issues as particulates remaining can travel deep into lungs compared to particle size pre dpf.
another case of misguided legislation similar to death of lean burn gas engines.

Would you really scrap a £5,000 car for the sake of a £700 repair? Do you get rid of cars when their tyres wear out? Anyway when drivers and mechanics stop being so dense the bills will become much rarer. DPF blocked? Replace it, oh look it's blocked again. Of course it is. Why is your engine producing more soot than normal and why is regen not working?

I think most 'failed' dpfs are some other problem. Don't see how it can fail, it's just a filter.

The real problem lies with the modern use of diesel cars, they are simply not designed to be used predomantly in town or for short runs, it clogs the filter which is designed to clean itself at sustained higher temperatures, unfortunately they are sold as a cheaper car to own even though they are dearer to buy & the running & fuel costs are higher

treaclesponge - Member

Wonder if that means Ill stop getting an advisory for having a plastic under tray every year as they will have to remove it to look.

Funny that one isn't it, my car had its 4th MOT yesterday at the same garage and passed fine but its the first time they have put 2 advisory's on the paperwork about undertray & engine cover, both OEM with the car.

A dpf is not a filter in the usual sense, nor is it quite like a catalytic convertor. Even if you drive all long motorway journeys and warm up the engine they can still become clogged, fail and put you in limp mode.

One cause of this is that a regen (which is when you see all the soot blow out) uses a liquid, if that runs out you get no warning until you end up in limp mode.

My 407 went from a 48 mpg average to 60 mpg once the dpf and egr were modified. Throttle response also greatly improved because the engine could now breath better. My car now never produces clouds of soot but yes it probably does chuck out the tiny particles you cannot see.

Having now read up on diesels and owned one I will be going back to petrol once the 407 goes. Cleaner, simpler and IMHO nicer to drive.

Funny that one isn't it, my car had its 4th MOT yesterday at the same garage and passed fine but its the first time they have put 2 advisory's on the paperwork about undertray & engine cover, both OEM with the car.

Makes a bit of a mockery of the whole thing really.I get one every time, without fail. Essentially they cant see the first 50% of the exhaust so it could be rusting away nicely and be none the wiser. Does that mean that if you have steel wheels and filled in wheel covers the brakes cant be seen then they cant check the pad wear?

I suspect that a modern diesel, even after having a DPF removed, is a lot cleaner than most 10+ year old diesels that I see chugging around with clouds of smoke around them. Oh and the portable diesel generator that turned Dartford into a foggy mess this morning.

The real problem lies with the modern use of diesel cars, they are simply not designed to be used predomantly in town or for short runs

Thta's not quite true. They are designed with this in mind, but you will get into trouble if you only do really really short runs. Or if you sit idling for ages If you drive around town all day you should be fine.

One cause of this is that a regen (which is when you see all the soot blow out) uses a liquid, if that runs out you get no warning until you end up in limp mode.

Only on some cars. If the DPF isn't hot enough to burn off the soot, the car needs to make the exhaust hotter. Some cars (VAG) do this by squirting fuel in the exhaust stroke, and a catalyst combusts these unburned hydrocarbons to increase the temperature enough to then burn the soot out of the DPF. Other cars (Peugot and Ford/Mazda) need this additive to do the job instead, and the catalyst is integrated into the filter.

My 407 went from a 48 mpg average to 60 mpg once the dpf and egr were modified

It'll also be producing loads more NOx too, which is a harmful irritant and causes smog. Nasty stuff.

I suspect that a modern diesel, even after having a DPF removed, is a lot cleaner than most 10+ year old diesels that I see chugging around with clouds of smoke around them

Probably not, it's probably the same. The engines work in the exact same way - squirt diesel into hot air - so if they are running at low load the results will be the same.

If you go back 20 years then injector pressures were lower and fuel atomisation wasn't as good, so at higher loads they produced more smoke, but under normal driving there's plenty of air in there so the fuel droplets combust more or less completely. That's why older diesels originally had much bigger displacement than equivalent petrol engines - more air to spread the fuel around in = less smoke.

If you floor a diesel from low revs there's a moment where the turbo isn't spooled up, so the ECU (to improve driveability) dumps extra fuel in there which doesn't burn completely, but still burns a bit to get the turbo going. This results in the puff of smoke you used to see. And I suspect that eco label diesels don't do this, which is why the reviews said that they had less low-end punch.

errrr....would it not be easier to ring up a few random MOT test stations in the area and ask them how they test diesels and what they look for? 😯

I've got a 90K 3 year old BMW 320d and it don't smoke one bit. It probably spits out cleaner air than it sucks in…

My car before that was a Toyota Avensis, when the outside temp got near 2 degrees or less it would idle at 1000rpm, I took it to garage and it's an emissions control thing apparently, Rev's highly to keep the coolant temperature up to prevent DPF from clogging up. Net result was it was doing 35mpg instead of reliable 42mpg, hardly protecting the environment is it's using loads more fuel!

[quote=geordiemick00 ]Net result was it was doing 35mpg instead of reliable 42mpg, hardly protecting the environment is it's using loads more fuel!

Depends which part of the environment you're trying to protect.

How long were you spending at idle for it to drop your fuel economy that much?

Anyway as has been said, this interrim technology is going to be replaced with something better in a few years time which will solve a lot of the problems.

Car speed has nothing to do with when a car regens its dpf, its mostly to do with exhaust temperatures due to engine revs. When the engine is cold the unburnt carbon from the combustion process is trapped by the dpf. When the engine is warm and the exhaust temps high enough the management system will trigger a regeneration process by altering the timing and ignition to burn the carbon and turn it into ash to be stored in the filter. When the filter is full its full and needs replacing. Lots of short journeys at low revs means more carbon in the filter full stop. Most modern diesels are so high geared that the revs never get high enough even on a motorway to regen fully. Manufacturers are moving the dpfs closer to the exhaust manifold to increase the efficiency of them but that leads to all sorts of design problems in the engine bay. Most regens are triggered at engine revs over 2000rpm and need at least 20 to 30 mins. If I was to buy a modern diesel it would be a year old and I would get shot at 4yrs old circa 60k.

trigger a regeneration process by altering the timing and ignition to burn the carbon and turn it into ash to be stored in the filter

I don't think that can be right. If you burn carbon in air you'll get carbon dioxide and water.

Your heating the carbon with the exhaust gases not air. There is no combustion taking place in the dpf just a heating process to convert the hydrocarbons to ash. The oxygen has been used in the cylinder when the charge combusts. What ever oxygen is left it must be CO2 and CO surely.

Oxygen is present in diesel exhaust at sufficient concentrations at practically all operating conditions.

http://www.dieselnet.com/tech/dpf_regen.php

Does that mean that if you have steel wheels and filled in wheel covers the brakes cant be seen then they cant check the pad wear?

No we can't, we can look the other side but depending on the size of the guard on that side you also can't see.

Wonder if that means Ill stop getting an advisory for having a plastic under tray every year as they will have to remove it to look.

No won't be allowed to remove anything, it's a no disassembly rule for mots.

I wouldn't worry too much yet, there are lots of things that get proposed and then never make it in, and even when they do make it in, it can only take a couple of days before it gets taken out again.

Regular sevicing with a good quality low ash oil, and appropriate additives with decent length journeys, and you shouldn't be seeing too many problems.

Why do you think the DPF and EGR are supposed to be there OP?

Your heating the carbon with the exhaust gases not air. There is no combustion taking place in the dpf just a heating process to convert the hydrocarbons to ash. The oxygen has been used in the cylinder when the charge combusts. What ever oxygen is left it must be CO2 and CO surely.

You're wrong on many levels.

Carbon particulates are trapped in the DPF, not hydrocarbons. There is a lot of 'air' in diesel exhaust as they burn very lean under normal conditions, also why they produce a lot of NOx (causes smog and acid rain) if you remove the EGR.

Combustion does take place in the DPF, the regeneration cycle begins by heating it up by injecting diesel (orother fluid) into the DPF, this then carries on combusting the carbon buildup untill it's gone.

There is little or no ash, ash is the unburnable (minearal, i.e. stone) component of a fuel, it pretty much only occours in coal (fairly high ash because it forms in stone obviously) and biomass. Liquid fuels will have incredibly small ammounts of ash as 1) they're very effectively removed by distilation, 2) there's very little to start with other than salt, which is removed by contact with fresh water and electroysis before it reaches the main part of the refinery.

"Whatever oxygen is left", there's a lot left as a diesel works at anything upto 1bar inlet pressure, a petrol engine works at atmospheric at most, at idle it's alsmost a full vacum (NA diesels and turbo petrols excepted, but they're rare, and still work under the same principals). Petrol engines work by combusting exactly the right ammount of fuel and air with a spark to ignite the mixture, all that (should be) left is CO2 and H2O. Petrol has a very high octane number to prevent pre-ignition. Diesel works by injecting a very low octane number fuel at just the right time into the cylinder (i.e comparable to the timing of a spark in petrol). The cylinder is full of high presssure air because it's inlet was atmospheric (or higher in a turbo), this makes it very hot, so as soon as the fuel is injected, it combusts. The reaosn you get carbon (soot) is the droplets burn from the outside in (unlike petrol where they very efectively vapourise as they spend a relatively long time swirling round in the hot cylinder before combustion and are far more volitile to begin with), and the inside has no contact with air, so cannot burn. So there is always a lot of excess air, even pedal to the metal at the redine there's still 2x excess air, often more.

The reason the EGR is there is to recirculate hot exhaust gas, this reduces the oxygen excess (without reducing the temperature and pressure, which is still required to burn the diesel) which in turn reduces NOx formation. NOx forms when there is excess oxygen at high temperatures and pressures, which is what you have in a diesel.

Thanks thisnotaspoon - that makes sense

Combustion does take place in the DPF, the regeneration cycle begins by heating it up by injecting diesel (orother fluid) into the DPF

Yes - there's another catalyst (besides the normal cat) either IN the DPF matrix or earlier in the pipe to create an exothermic catalytic reaction with either the hydrocarbons or the urea additive to increase the temperature.

NA diesels and turbo petrols excepted

Always air present even in NA diesels. You can't mix the diesel and air well enough to mix all the air evenly with diesel.

Diesel works by injecting a very low octane number fuel at just the right time

Not sure diesel would count as low octane, if they measured it that way...?

Otherwise bang on though 🙂

Ford have seen a drop off in diesel engined sales as a result of DPF issues. They are introducing 'technology' on new diesels that will heat the DPF from start up to make it work on shorter journeys.

Nice.. electrical heating? Or some kind of fuel burner?

Ford have seen a drop off in diesel engined sales as a result of DPF issues. They are introducing 'technology' on new diesels that will heat the DPF from start up to make it work on shorter journeys.

I'd venture its also because small petrol engines are becoming a lot more effecient

If you haven't seen it, this is part of an article about MOT fails on PistonHeads this morning.

Still to come are requirements to fail a car on a lit engine management light and also to fail diesels if a factory-fitted particulate filter has been removed. This comes into force next month and might scupper anyone who's had theirs whipped out by any of the companies offering removal service and ECU reflash. However you might get away with it if the job's a clean one. A spokesman for the DVSA told us that rather than check via computer whether the car was fitted with a DPF it's "a visual inspection of the exhaust system".

Still to come are requirements to fail a car on a lit engine management light

I'll be in the shit then 🙁 I think that's outrageous - some EMLs are nothing remotely to do with safety.

I'd venture its also because small petrol engines are becoming a lot more effecient

Yes, and people are learning where diesel's appropriate and where it's not.

Not sure diesel would count as low octane, if they measured it that way...?

Thats why it burns with no need for a spark.

typicaly ocyane goes down with increacing molecular weight, which is why petrol goes off in the tank as the butane evaporates leaving low octane stuff behind. You can build very high compression LPG engines for this reason.

Thats why it burns with no need for a spark.

Well you are right about the octane number, but that's not the reason diesels don't have a spark. The fuel is chosen because it suits compression ignition, not the other way round 🙂

People are working on comression ignition petrol engines.

[url= http://blog.caranddriver.com/hyundai-developing-gasoline-burning-compression-ignition-engine/ ]This is cool - compression-ignition petrol engine[/url]

Just think of all that green fail,

Think you're mixing up your arguments. A lot of these devices are required to be fitted, knowing that they will *decrease* the fuel efficiency, in order to reduce emissions which are harmful to health when released in congested cities and so on.

NOx (EGR) and Diesel Paritulcates (DPF) mainly cause health problems.

Excessive CO2 released from fossil fuels causes climate change.

Unnecessarily building and scrapping cars because they need a new DPF (it that's happening) probably causes more Co2 but not much Nox or DP.

Unnecessarily building and scrapping cars because they need a new DPF (it that's happening) probably causes more Co2 but not much Nox or DP.

Yes and almost certainly not near the ground in city centres where kids breathe it in.

Why do you think the DPF and EGR are supposed to be there OP?

Well, I now know [i]exactly[/i] what they are there for...

When the car went wrong and the garage quoted £600+ to repair and warned that I could see another failure within a year or two (apparently thats not unheard of) they suggested I could bypass them for a lot less and get an improvement in economy that would offset the cost of the bypass.

When I asked what they did I was told it all lowered CO2 emissions, and given my car had quite low emissions anyway I was happy with that explanation.

The economics were simple though - would you pay £600-£700 on a 9 year old car with 90,000 miles plus on it knowing that you could face the problem again, or get them removed and plan to run the car into the ground over the next 2-3 years?

Even knowing what I know now about the EGR and DPF I believe I still made the right choice and saved a car from the scrap yard. IMO the technology as implemented on my car in 2004 was not proven and the move towards diesel by many on the basis of better MPG was poor judgement.

The question is, why would it fail again? There has to be an underlying cause as to why the DPF got blocked up.

I do spend money on old cars, because if you take market forces out of the equation there's no difference between an old car and a new car. Just because people arne't willing to pay much for it doesn't mean it's any less valuable as an object.

There was no reason your car would be junk after 12 years anyway. It costs money to look after yes, but nothing like as much as a new car costs to buy. The low monetary value of old cars has consigned far more cars to the scrapyard than any technology has.

Well I'm certainly happy to spend money on older cars to keep them running but you do have to call a day when you could potentially buy another older car that has been well looked after.

At the time I had to take what the garage told me as I had a knackered car and not a huge amount of time available ergo - get it fixed as economically as possible or sell for spares/repair.

I've since learned that for my 407 the most likely cause was it running out of some fiendishly expensive liquid used by the DPF for a regen cycle - there is nothing on the dash to warn you this has all gone and its not a self service item either.

On the plus side I've also been told that as my car is a 1.6HDi the EGR bypass should help keep whatever bits cleaner that contribute towards turbo failure. Whether this is a fact I'm not sure, but sounds plausible.

The car now drives great and it'll be kept until it becomes cheaper to buy something else than fix - hence my earlier comments about switching back to a NA petrol engine when the time comes.

To bring back an old post:

Has anyone had a car with DPF removed tested yet?

Did it pass or fail?