Service Issues: XC90 D5 engine DPF (Diesel Particulate Filter)

[shimon340]

hi there

sorry to hear of your problems with your filter on the xc90.

having worked on dpfs ( research dept ) I think I can help out here.

Basically, the diesel particulate filter ( dpf ) is effectively a fine mesh placed in the exhaust. It catches diesel particulates (soot). The filter is also coated with some metals which act as a catalyst to burn the soot. The catalyst lowers the temperature at which the carbon / soot combusts. This therefore removes the soot from the exhaust, lowers the vehicles particulate emissions and therefore allows compliance with Euro 4.

however, the filter is like a catalytic converter in that it is actually a blockage in effect in the exhaust. The engine has to "push" the exhaust gas through the filter and this increased engine load ie the engine has to work harder. Making the assumption (which most likely isnt true) that the engine control programme for Euro 3 and Euro 4 was identical, a Euro 4 vehicle would have lower engine output / power and higher fuel consumpion and higher CO2 emissions ( from the burnt soot ) but lower particulate, hydrocarbon emissions than a Euro 3 vehicle. Almost all manufacturers re-write the engine programs ( called maps ) for Euro 4 to improve engine output and therefore keep power and CO2 emissions the same. more often than not CO2 emissions will be a bit higher for a Euro 4 engine as one engine emission ( soot and HC hydrocarbon ) has been converted to another ie CO2.


The vehicle has a "back pressure sensor" mounted in the exhaust ahead of the dpf. This gives information on how "blocked" the filter is. The dpf has metals to catalyst the oxidation / burning of the soot but this temperature is still higher than the exhaust gas temperature at idle. Exhaust temperature increases with engine revs - idle gives the lowest temperature.

So, with todays dpfs it is 100% possible for vehicle use and driving style to mean that the filter doesnt regenerate sufficiently during everyday driving.
This is due to current dpf technology meaning that the "light off" or the temperature at which regeneration occurs is too high and the filter doesnt regenerate sufficiently during town driving. This affects all manufacturers.

Systems will lower light off temperatures are not currently on the market as they are not sufficiently durable and either fail a vehicle manufacturers testing programme or fail to meet the American emission standards which give a time lifespan of the filter over which time its efficiently must not drop below certain %.

So, your vehicle will regenerate its own diesel filter if the exhuast temperature is high enough.

Alternatively, there is a backup fitted.

When the back pressure sensor triggers the fact the filter is sufficiently blocked it should activate a "fuel rich" engine control map. This runs the engine richer than normal increasing exhaust temperature and regenerating the filter.

If the filter fails to clear, the back pressure will still be too high and then the warning message will appear. The filter then gets manually regenerated ie heat with a heat gun!!! by a dealer or drive the car above a certain rpm for 15 mins. Interesting, the Renault laguna manual states "if the regenerating message is displayed, please drive the vehicle above 40mph for 15 mins" interestingly, this vehicle is "illegal" on the island of Guensey since the max speed is 30mph!

Your xc90 manual should say what revs are needed for what time to regenerate the filter. BUT, on the volvo this is only a back up to the self regeration!

So, your car fail to regenerate itself. you may wish to get the back pressure sensor checked. it maybe failing to respond early enough to activate the regeneration.

The diesel engines in the S40 /V50 are Ford/Peugeot 2.0 units. Im not sure if they use a cerium based additive. This is basically a metal injected into the exhuast to act as a catalyst to burn off the particulate matter. Renault also use a cerium based additive.

I would be surprised if Volvo is doing this in the S40 but the system was inherited from Ford so they probably had the choice of "use this cerium additive or dont have any Euro 4 diesel engines in the S40 range!"

From my time at Volvo trucks, my research was to find non-toxic and non precious metal catalysts which could be used. Volvo was against cerium due to its high toxicity...and didnt want it being released from the vehicle exhaust

hope you xc90 is sorted soon!

Ps the note you have about "every refuelling". There has been a bit of chinese whispers with that message. They most likely mean after consumption of a whole tank of fuel the filter will need regenerating - if the system doesnt self regerate with the rich cycle. they dont mean after every time you top up the tank

hope that helps. please keep me posted

S

[Jet2 D5]

Originally Posted by shimon340

hi there
So, your vehicle will regenerate its own diesel filter if the exhuast temperature is high enough.

Alternatively, there is a backup fitted.

When the back pressure sensor triggers the fact the filter is sufficiently blocked it should activate a "fuel rich" engine control map. This runs the engine richer than normal increasing exhaust temperature and regenerating the filter.
S

Hello Shimon
Very interested in your comments, if you have read my 1st post on this forum you will know I am unhappy with the imposition of the current DPF workings and guess the S60 185 bhp is the same system/software as XC90.

While not suffering from blockages my regeneration cycle is every 400/550 miles and infer from you comments it always works via the backup system as fuel consumption approximately doubles and the engine gets very hot. I do little city driving, on 15/25 mile legs the cycle can spread over 3 or 4 journeys equating to 50 miles/90 min at operating temperature. Best ever achieved - 20 miles at 60 mph keeping in 5th gear.

As I am told there is nothing wrong with my car (how they know is not forthcoming), do you consider it should regenerate without fuel rich mapping at normal fuel consumption on at least some occasions?

[shimon340]

hi there!

it sounds like your car is regenerating the filter via the rich map solution. I cant comment on the exact details of volvos ECU software ie the frequency of the rich cycle etc but your car will use this if your usual driving style doesnt generate sufficiently hot exhaust temperatures. such is the situation with current dpf technology - the light off temperature is still too high.

a lot of town driving, low revs etc would mean the vehicle failed to obtain sufficiently high exhaust temps for regeneration meaning the vehicle would need to go into a rich map mode. The length of that mode and frequency maight be published in general terms in the research literature of SAE for example but the exact details of the map are probably not in the public domain.

what sort of driving do you usually do? the enrichment is only a slight change and should have an significant impact on fuel consumption

[Jet2 D5]

Originally Posted by shimon340

hi there!

it sounds like your car is regenerating the filter via the rich map solution.

a lot of town driving, low revs etc would mean the vehicle failed to obtain sufficiently high exhaust temps for regeneration meaning the vehicle would need to go into a rich map mode.

What sort of driving do you usually do? the enrichment is only a slight change and should have an significant impact on fuel consumption

Hi Simon
Thanks for yours, see you were up late again.
The car does around 8000+ miles per year; journeys are very consistent each week and cover legs of between 15 & 25 miles with the odd trips of 70/90. As stated regeneration cycles vary from 400/550 intervals but usually cover multiple journeys, the shortest time (isolated) has been 20 min when I left it in 5th at 50/60 mph.

The claimed time of 10- 20 minutes seems a nonsense, for info quote a statement from the Master Mechanic after discussion with Volvo Tec “Regeneration can be triggered in several ways: consumed fuel volume, differential pressure over particle filter or calculated particle weight in the filter. The calculation is made by the engine control module (ecm) and is based on the engines driving circumstance. the particle filter filters out more than 95% of the exhaust particles, after approx 310-621 miles the particle filter is full and needs to be cleaned (regenerated).regeneration is started and carried out automatically while driving takes 10-20 minutes depending on the driving style the factory are now asking why do you think engine temperature is excessive (have you seen any warnings in display) because it has been tested to cope with this”

I have never seen what you might call short regenerations, every time 100+ miles are wiped off the distance to empty in a very short time and cannot be optimistic on engine component durability with frequent high heat generation.

Certainly I would have stayed petrol given what I know now, even with the 6th gear the fuel economy must be much inferior to the old D5 and from what you say Euro IV is probably inferior to Euro III, although doubt this needs to be the case if Volvo got their act together. What a pity this technology appears to have been inflicted on an unsuspecting Joe Public!

[shimon340]

hello!

I havent actually worked on the D5s diesel filter regime so I cant comment on the frequency of the regeneration that volvo have decided for.

Basically, the system looks for the back pressure increasing and when it passes a certain value, a regeneration period is planned. As above from me and your volvo mechanic your vehicle is regenerating the filter by this route due to the type of driving you do. ( I presume the dealer has been asking volvo tech for some assisitance. As you can see above, volvo tech can contact the development team and the factory very easily - volvo is highly organised in this manner and the flow of tech info is excellent with the company. I speak from experience from othe manufacturers who simply dont have this organisation or detailed archives, service manuals etc )

During higher engine speeds and higher exhaust temperature periods, the filter will regenerate automatically simply because the filter is above its light off or catalysis active temperature. However, prolonged periods at lower exhaust temps counter this affect. I cant give exact figures here but there is a balance between the rate of regeneration due to higher temps and filter blocking due to too low exhaust temps. To put it another way, its like filling a bath with the plug open. some driving styles or times ( called duty cycles ) will result in higher temps eg motorways, and other like town driving will simply fill the filter. Even when the exhaust gas temp is high, the filter wont be empty. By the nature of its design, the filter collects particulates to later burn them off. It doesnt burn them faster than they are produced normally so a regeneration will be needed from time to time even if the car were to only do motorway driving. Maybe that helps you concern?


With regards to the rich cycle, your distance to empty or rank and the engine temperature.

ok. distance to empty. This is calculated based on the volume of fuel in the tank and the average fuel consumption ( some systems will use the instanteous fuel consumption but this leads to frequent changes in the range each time you accelerate hard etc ). Practically, the system will recalculate the average fuel consumption after a certain time period, and then adjust the range accordingly.

When the engine management goes into rich cycle, the instantaneous fuel consumption will fall ( higher fuel rate usage so lower mpg ). This will in turn affect the average fuel consumption and hence the range. once the rich cycle finishes, the on board computer for fuel consumption and range short change values due to the now lower fuel consumption.

engine temperature. The light off temperature for a diesel particulate filter depends on its design so I cant comment on the exact spec for the D5. The exhaust gas temp is affected by engine speed, load as well as ambient conditions since the exhaust cools as it travels down a cold exhaust.

you engine will run slighly hotter due to the rich cycle to increase exhaust gas temp. What increase in temp are you noticing? The vehicle will be keeping a check on the coolant temp so there is no detrimental affect of this. higher temperatures are not of concern so long as the temperature does not approach the engine overheat limits - if it does then there is something else wrong with your vehicle. The rich cycle is to increase exhaust gas temp but not engine temp - this will be kept in check by the cooling system. Also, the excess fuel which doesnt burn also aids regeneration by small fuel droplets landing on the filter, oxidising, creating heat and local hot spots in the filter which then heat it from the surface causing soot to ignite and thus further heat the filter promoting regeneration.

in regards to your concern of volvo not having their act together and euro 4 being worse than euro 3... let me elaborate

Vehicles produce a host of emissions ie classes of chemical compounds. Emission regulations aim to set maximums for certain classes eg nitrogen oxides, particualtes, hydrocarbons, sulphur oxides etc.

Euro 4 requires a decrease in particulates and NOx. This is the area I most recently worked in for volvo. TO reduce particulates and hydrocarbons, you can make the engine run hotter - ie be more fuel efficient by more fully burning the diesel. However, the higher temperatures increase NOx emissions.

NOx and HC / Particulates are like a see-saw, it is difficult to lower both.

For Euro 4 particulate filters ( some manufacturers had to use them to get their vehicles to meet Euro 3 too! ) are used to trap the particulates. However, the extra load on the engine ( engine needs to push the gases through the filter ) will naturally increase fuel consumption. Further, if fuel consumption is measured by the CO2 output per km or mile, a Euro 4 vehicle with a particulate filter can often produce more CO2 than a Euro 3 vehicle. Why? Isnt Euro 4 cleaner? Yes Euro 4 is, but you need to look at the total emissions profile of the engine. As more particulates and HC and CO ( carbon monoxide ) are removed from the exhaust by being oxidised/ burnt, you are creating more CO2 which would have otherwise have left the engine as CO, HC particulates etc.

Careful development and testing of the engine control programme ( called a map ) means that a manufacturer can produce a Euro 4 engine with lower fuel consumption than a Euro 3 engine - it just takes more work! There are other changes and developments to a Euro 4 engine that can be used but not all manufacturers use these.

So since emission regulations are a balance between numerous factors including fuel consumption, power, torque etc you can see why this is a complicated business, more than seems apparant from the standard published fuel consumption and CO2 figures.

Volvo is not alone in using the enrichment mode for regeneration so there is no fault to volvo for this system.

Further, whilst lower light off temperature diesel particulate filters ( dpfs ) are available, currently none on the market meet the durability ( certain % activity over a given time / mileage ) criteria also included in emission regulations

trust me, all manufacturers dream of a continuously regenerating diesel filter which regenerates even when the engine idles. A diesel filter currently collects particulates, burning them off whenever the exhaust temp is high enough. Unlike the catalytic converter of a petrol engine which doesnt store compounds for long periods, current dpfs dont operate such a "passing through, non storage" process so inherently need a regeneration from time to time

how long are the regenerations lasting and how are you assessing it? to judge by fuel consumption or range wont work since the on board computer doesnt sample at a higher enough frequency so their will always be some delay it is fuel consumption and range figures re adjusting once the rich mode is finishes. Where I currently work, the onboard driving computer only resets the average fuel consumption at the end of every trip. leads to some confused people! volvos isnt like this I believe.

hope this helps!

please ask any more questions you have

kind regards

shimon

[Jet2 D5]

Originally Posted by shimon340

you engine will run slighly hotter due to the rich cycle to increase exhaust gas temp. What increase in temp are you noticing?

Careful development and testing of the engine control programme ( called a map ) means that a manufacturer can produce a Euro 4 engine with lower fuel consumption than a Euro 3 engine - it just takes more work! There are other changes and developments to a Euro 4 engine that can be used but not all manufacturers use these.

How long are the regenerations lasting and how are you assessing it?

shimon

Hello Shimon

Firstly thanks again for your lengthy post, appreciate your explanations and feel sure others will likewise.

Regeneration periods have been as long as 56 miles taking 106 min (multiple journeys) to best as stated, average of last four gives 42 miles/70 min. It is quite easy to see when occurring from the instant read out, majority of my journeys repeat and I could quote ranges either way on specific roads where the same speeds and gear applies. Journeys are 15/25 mile legs mainly off peak on A roads with an average 70/90 mile trip each month.

To answer excess temperature, the water is of course constant, however if you stop during regeneration it only needs the window opening to recognise the hot smell. Open the bonnet and phew! - put a hand on the top of the plastic cam belt cover (which is open on one side) and you would move it pretty dam quick.

Notice Renault were introducing a particulate filter with exhaust post-injection on the smaller models - in their marketing it stated existing particulate filter systems in passenger cars have relied on engine (rather than exhaust) post-injection to enrich the exhaust gas in hydrocarbons and increase the temperature. This approach, while not requiring the additional exhaust injection hardware, has certain limitations in conducting filter regeneration at very low engine loads. Engine post-injection can also have a detrimental effect on engine durability due to the oil dilution effect on cylinder walls during late cycle fuel injection. So my thoughts are also in line about shorter component life.

At the end of the day through lack of available knowledge at purchase I have an expensive car that spends around 10% of the time regenerating the filter at 50% reduction in mpg - when Gordon Brown recognises this - expect a further tax on Euro 4. The consensus seems to be that Volvo Euro 4 is inferior to 3 for mpg, you say this need not be the case, so live in hope Volvo can improve the software.

[Razer]

This all makes for very interesting reading as i am going to test drive an S60 (185bhp) tomorrow with a view to buying it. Most of my journeys are also short in duration with the odd bit of motorway driving with the car in the garage most of the week as i live close enough to work to walk. Does the information centre tell you when a regeneration si taking place? or is this all from the fuel consumption? Also is it possible to force a regeneration for instance if you know you are going on motorway for the next 50 miles for instance?

Should i let this put me off the 185bhp version? as i have already looked at the 163 D5 and boys being boys would obviously prefer the more powerful version.

[GMcL]

Very interesting reading this as I bought a Euro3 two months ago based on the fact I didn't like the fuel consumption figures people at work, driving comapny cars, were quoting for Euro4's.

Two things strike me from reading this thread.

1. If you only intend using the car for very short journeys why buy diesel ?
This doesn't make sense as diesel engines work better for long distance work, medium engine speeds and preferably under load.
Petrol is by far the better option, as it warms up faster, for frequent short journeys although exhausts do suffer from condensation build up.

2. If such high exhaust gas temperatures are required for regeneration, in combination with enriched fuel mapping causing droplets of fuel to come through the exhaust, I wonder how long the exhaust valves on these cars are going to last.

[Razer]

Originally Posted by GMcL

Very interesting reading this as I bought a Euro3 two months ago based on the fact I didn't like the fuel consumption figures people at work, driving comapny cars, were quoting for Euro4's.

Two things strike me from reading this thread.

1. If you only intend using the car for very short journeys why buy diesel ?
This doesn't make sense as diesel engines work better for long distance work, medium engine speeds and preferably under load.
Petrol is by far the better option, as it warms up faster, for frequent short journeys although exhausts do suffer from condensation build up.

2. If such high exhaust gas temperatures are required for regeneration, in combination with enriched fuel mapping causing droplets of fuel to come through the exhaust, I wonder how long the exhaust valves on these cars are going to last.

Well in relation to point one in my case is that i fell in love with the D5, i love the idea of having that extra oomph when required, with absolutely no effort involved. I normally do around 12k a year, but at the moment im doing around 30k, but this isnt for much longer.

2. very good point.

[GMcL]

Originally Posted by Razer

Well in relation to point one in my case is that i fell in love with the D5, i love the idea of having that extra oomph when required, with absolutely no effort involved. I normally do around 12k a year, but at the moment im doing around 30k, but this isnt for much longer.

Nothing wrong with buying the car you want, just be aware that diesels used in frequent short, stop/start journeys where they aren't getting upto temp require more servicing.

If I were in the position to be able to afford a D5 Euro4, there's no way it would be going 18k between services (in particular oil changes). Even with modern long life synthetic oils which are supposed to trap the rubbish. I'd be slipping an oil & filter change in at 9k. Which is an additional expense.

I find it quite amazing that Volvo are giving the diesels an 18k service interval.
Audi will stick you on an extended service schedule (anything upto 20k between services) for their diesels but, it's a well documented fact their TDi engines sludge up and can have internal timing chain problems, at about the 70k mark, if not treated to a new filter and oil change every 10k.
The French, who are pretty good with diesels, stick with a 12k stop for diesel vs. 20k for petrols.
I currently cover about 12k per year and will be having a 6k oil and filter change as it's cheaper than desludging and rebuilding an engine at the 5 or 6 year MOT due to poor emissions.