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…?

yep, diesel is typicaly a RON of 15-18 compared to arround 92-100 for petrol.

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.

This is cool – compression-ignition petrol engine

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 exactly 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?