Diesel Particulate Filter

[joseph3000]

MB dpf technology uses a pressure sensor to monitor the pressure differential either side of the dpf. also 2x temp sensors, one before and one after the dpf. also 1x lambda sensor mounted before the cat (ie before the dpf). if one were to remove the dpf it is fair to assume that the ecu would notice from temp sensors and pressure differential sensor that all was not well. however it may well be the case that the ecu could be given a new scn (change coding to say no dpf fitted) to run without, ask me in a couple of years!

hi,I have 315 sprinter 2007 falt code 2079 (diesel particulate filter differntial pessure sensoe)engine protection is active,I use star machine,any help
cheers

 

[davidczcars]

Just a note on the peugeot particle filters we used to take them out and power wash them in the reverse of the exhaust flow and they were purfect for many thousands of miles after this i dont know if its of any help but we did not need to regenerate as this used to need very high exhaust temperatures,

 

[Alex Crow]

and what does star recommend for that code? is it a sensor issue, or just the dpf has too much ash? star is a great tool, just follow the guided tests and read the info on star and wis.

 

[djcheung]

Hi All,

I also have a 05' S320 CDI with DPF installed.
It has been a long battle with MB trying to get to the bottom of why it is regenerating so frequently - once every 60-80 miles.
They have 'replaced' everything relating the regeneration - dpf, pressure sensors etc but still has not improved the symptoms.
My average daily journey is mixed with town and motorway.
MB says everything is working as it should.
If everything is working as it should, then would it be the engine is pumping out excessive amount of pollutant that clogging up the dpf and triggering the regeneration?
With a dpf, you can hardly see any smoke. How can you test it?

Or there is something else that isn't quite right.
It drives ok and no loss of power. Average 34-36mpg.

I am trying to loan a STAR machine from MB to plug in, and record any measurements while driving and see if I can make any sense out of them.

Anybody here has any info is much appreciated.

Thanks,

David.

 

[Varco]

S320 CDI L 2008 FITTED WITH DPF


OIL CHANGE AT 15000 FIRST SERVICE; SHELL HELIX 229.5 OIL WAS USED I.E. NOT LOW ASH 229.51.

MERCEDES PUT IT THROUGH DIAGNOSTICS; ASH 15%/ SOOT 77%/ BACK PRESSURE 1027 hPa.

TOLD WAS FINE AND DRIVING WOULD GET RID OF ASH/SOOT.

QUESTIONS; IS IT FINE?
ASH IS THERE FOR GOOD-RIGHT?
ASH IS NON COMBUSTIBLE-RIGHT?
SO LIFE OF FILTER REDUCED-RIGHT?
BACK PRESSURE; IS IT HIGH?
SHOULD I PUSH FOR REPLACING OF DPF AT THEIR EXPENSE?

SINCE OIL CHANGE TO 229.51 MPG FALLEN 20% ?WHY

Soot comes out of the engine in the form of solid and liquid particles. The liquid particles are rapidly dispersed by exhaust heat. The DPF will thus trap solid soot and ash, and evaporate off any remaining liquid particles. Raising the temperature of the DPF (by driving hard) to around 600 deg C will cause the soot to oxidize (burn) in the presence of O2 and turn into CO2 which is released from the tailpipe. (Additives can be added to the fuel to lower the regeneration temperature - Peugeot do/did this) To collect the soot the DPF is a large porous surface made from a ceramic, the maximum surface area is gained by making the internal of the DPF like a large bundle of porous tubes. Soot coats the tubes as the DPF traps it. Regeneration is triggered when there is enough soot (too much and the DPF will get too hot = crack when it regenerates). Determining how much soot has been trapped is usually done by measuring presure difference across the DPF or estimating how much soot has been created (= trapped) as a mathematical function of fuel burnt. The allowable pressure difference across the DPF will vary for many reasons and guidelines for 'good'/'bad' are likely to be specific to the DPF and/or use.

Regenerating requires sustained high temps, so the regenerations are best done at crusing under load. Doing the regeneration stationary risks temps getting too low and the soot not burning efficiently. Low speed (or stationary) regens are often supported by 'post injections' which mean adding additional fuel to the cylinder close to the exhaust valve opening point - this fuel burns on the DPF raising temps high enough for regeneration - the fuel creates no 'power' in the cylinder. If the additional fuel does not burn (for what ever reason) you can get white/grey smoke out of the exhaust caused by incompletely burnt fuel, this is 'not good' and should be avoided. My advice - Take your car for a good high-speed run (does not need to be 'banzai') to be sure of a good regen - on the plus side this is another good reason to take the Merc out for a 'quick' drive

Ash in the oil, and microscopic amounts from the fuel, will accumulate in the tubes ('channels') of the DPF. Ash does not burn and hence regenerations will not remove it. It should build up slowly over time if low ash oils are used. As the ash builds the storage capacity of the DPF falls, worse than this the distribution of soot deposits can change leading to greater risk of DPF cracking. The ash will also raise the pressure differential across the DPF making regenerations more likely and increasing fuel consumption.

If the DPF is removed it should be possible to remove most (likely not all) of the ash using compressed air or similar flowing the opposite way (!) to the exhaust flow. However, exhaust systems seem rarely to be designed with this thought in mind so making it happen might be more tricky than it sounds. Using a pressure washer should work in theory. With any cleaning and/or servicing be careful not to damage the DPF ceramic as the OBD system should be set up to detect even a tiny leaking crack or puncture and will set a MIL light.

I'm not sure (although I can guess) how the diagnostics estimate 15% ash in your case and this does sound very high but (as with all statistics) could be because there is little soot in the DPF - eg straight after a regen ash/soot percentages could be 99.5/0.5 . Are the percentage figures related to the capacity of the DPF? Did the diagnostic system say how 'loaded' the DPF is/was, for example a mass in grammes or grammes/litre? Understanding these points would help interpret the figures.

Finally (!), how long did you drive with the 'high' ash oil? The ash content of a normal (eg not low-ash) oil is still low in percentage terms and you can only get it into the DPF by burning the oil in the engine. Assuming that you only drove on the 229.5 for one oil change interval and you didn't consume much oil during it, it sounds unlikely that ash is the cause. Excessively high back pressure could well explain the fuel consumption you are seeing but there are lots of other causes possible. I would take the car out and give it a high speed run to regenerate the DPF (or ask Mercedes to trigger a regeneration) and ask them to re-check the figures - backpressure should have dropped if the problem was soot alone.

 

[Alex Crow]

good reply varco, unfortunately the poster that asked the question has not been on the forum for 17 months

 

[madeinmanchester]

Alex Crow = Mercedes God!

Just to say Thank You to Alex Crow

Took my 2007 S320 stuck in limp mode.

Found him on this forum after searching the internet to fix my fault.

Phoned him, took my car and he fixed quite a complicated DPF Fault.

Found and changed an exhaust back pressure sensor in minutes!

HE IS THE MERCEDES GOD!

A true expert!

Honest guy with good prices!

Will never take any mercedes anywhere else ever.

Thank You, see you next time!

 

[Eddy Jawed]

I had a big costly problem with DPF. I took bad advice from a back street mechanic who diagnosed it with computer and told me to drive on motorway. The fault stated was 'The regeneration Frequency of DPF is not OK'.... Completely vague stupid description. Annoyingly car dash never said anything about DPF getting blocked or % close to blocking like you see in other cars and just showed a engine management light.
Anyway I drove on motorway and after 15 minutes back pressure caused by blocked DPF driving at 80mph blew the engine. Now I need to replace the whole engine and its costing around £2.5k. Really gutted and angry at Mercedes for not adequately warning drivers about DPF problems. I was doing a lot of city runs which clogged it but it was only 3 weeks driving. Ridiculous things added by out of touch EU politicians in Brussels hurting motorists really hard.

 

[LostKiwi]

I don't see how back pressure can blow an engine. I suspect you had another issue already that was causing the blocked DPF.

 

[Taffy7hfa]

I stuck a potato up the exhaust pipe of my old series 1 Landrover once, didn't blow the engine up though