DPF levels and regeneration - Page 2 - Club Touareg Forums
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post #11 of 93 Old 01-17-2019 Thread Starter
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Originally Posted by seafarer28 View Post
Hi Singh,


Good pick up, the last reading is from my "new" '08 with 100K kms on the odo, all the other readings came from my previous one which had 220K on disposal in 03/2018, no maintenance ever done to DPF.


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post #12 of 93 Old 01-17-2019
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Originally Posted by nickyt View Post
The system does not want the ash level to go over a certain percentage.
That's soot, not ash. Ash level can only increase, never decrease, as that's the part that remains in the DPF after the it has been regenerated. If a regeneration completes, soot load is considered to have returned to 0%. However, ash levels never decrease, and when they reach a certain limit, the DPF is considered full/blocked and MUST be replaced. There's no other remedy for this.

Well, the DPF can be theoretically cleaned or even deleted, but this is not official repair method, and involves essentially the same process as the replacement of the DPF, except of course not every part of the DPF will be actually put back on or put back on new.

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All is not lost at that point, the system will still try to initiate a burn. A long highway trip is perfect and the burn is started. But, the computer monitors the burn temperature. The more ash you have to burn, the hotter the burn. Once you hit a certain temperature, the system will shut down the burn.
It's not the temperature that stops regeneration - even though there might be fail safes for temperature, too. But generally a DPF regeneration, once initiated, should never reach temperatures that trigger such a shutdown - unless there's something wrong with the car. Instead there are two other things that can prevent or stop regeneration.

One of them is, that the cars cruising speed or the engine speed falls below a certain threshold (30-60 km/h, 1500-2000 RPM, depending on model), that's required for the regeneration. If this happens, this will not trigger a fatal condition per se, because the regeneration will be resumed when the car has speed up to required cruising speed again. The only problem that can arise from interrupted regenerations is, that soot still gets accumulated until it can be resumed, and trigger the other condition explained below.

The other condition that will prevent from the regeneration being initiated (or resumed) in the first place is, when the _soot_ levels are beyond a certain threshold. This might be 40 to 80% depending in the actual DPF. The regeneration will not be initiated because the burn temperatures would be too high in this case, and it could possibly result in the car catching fire or taking heat damage.

If this happens, but soot level is still below a certain limit (usually <75-80%) a manual regeneration can be initiated by service personnel through VAG-COM. Then they can monitor the process and abort if needed. However, if soot level goes above said limit, regeneration will not be allowed even this way, and the DPF will have to be replaced.
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post #13 of 93 Old 01-17-2019
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Quote:
Originally Posted by seafarer28 View Post
Here's some VCDS DPF data taken from my 2008 3.0Tdi
The maximum allowed ash volume for that particular model (presumed it's a CATA engine) is 0.46. So, at 0.3 the DPF is already at 2/3 of its theoretical lifetime. Just FYI.
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post #14 of 93 Old 01-17-2019
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Quote:
Originally Posted by Gnits View Post
The maximum allowed ash volume for that particular model (presumed it's a CATA engine) is 0.46. So, at 0.3 the DPF is already at 2/3 of its theoretical lifetime. Just FYI.

No, the engine is a CASA not that it would make any difference at it probably has the same DPF components fitted.


This is the first time that I have seen any ash levels quoted on the subject, do you have a reputable source for your quote?


thanks,


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post #15 of 93 Old 01-18-2019
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Originally Posted by seafarer28 View Post
No, the engine is a CASA
Same difference.

Quote:
Originally Posted by seafarer28 View Post
This is the first time that I have seen any ash levels quoted on the subject, do you have a reputable source for your quote?
Is the original VW maintenance service manual reputable enough for you?
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Thats what i understand. Soot is regenerated and results in ever increasing Ash.

Also, Whats the difference between calculated vs measured soot levels?

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Quote:
Originally Posted by Singh View Post
Thats what i understand. Soot is regenerated and results in ever increasing Ash.
Correct.

Quote:
Originally Posted by Singh View Post
Also, Whats the difference between calculated vs measured soot levels?
I think both of them are in a way calculated, but the "calculated" one is a rolling sum over time, that's based on fuel consumption, air intake, lambda measurement data, and calculates the theoretical amount of soot generated, while the "actual" value is calculated using the momentary difference in the exhaust gas pressure before and after the particulate filter. But don't quote me on that.

Anyway, I think it's kind of a self-check or fail-safe. The two soot load values are calculated using different methods, so that if the sensors involved in one start delivering false values, the ECU will notice the difference, and instruct the driver to have the vehicle serviced, and will refuse to start regeneration. This is likely important, because as said, starting regeneration on an "overloaded" DPF can cause the engine to catch fire - so, it makes sense to have the load value double-checked, just to be always on the safe side.

It might be also intended to prevent trivial tampering with the DPF (ie. delete).
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Quote:
Originally Posted by Gnits View Post
Same difference.


Is the original VW maintenance service manual reputable enough for you?



Great, thanks!


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post #19 of 93 Old 01-18-2019
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You guys have done some great work here. As I said, it had been a long time since I read the theory paper. As promised, it was sort of close. Thanks to all who filled in the gaps.

According to the SSP, there is a pressure sensor both before and after the DPF. There is also a temp sensor both before and after the DPF.

Here is a SSP guide that should help explain what is going on.

http://www.volkspage.net/technik/ssp/ssp/SSP_336.pdf

Quote:
Frequent short trips
For the regeneration process to be initiated in the diesel particulate filter, the exhaust gas temperature is increased by the engine management system. In the event of frequent short trips, the exhaust gas temperature cannot reach a sufficient level. Regeneration cannot be carried out successfully. Subsequent regeneration procedures that are carried out with excessively high levels of carbon soot deposit can lead to overheating and damage to the particulate filter. The filter could become blocked due to a high level of carbon deposit. This blockage in the filter could cause the engine to fail.

In order to prevent these cases from happening, a diesel particulate filter warning lamp will be activated in the dash panel insert once a specific limit is reached in the filter storage capacity or after a certain number of unsuccessful regeneration procedures.

The driver is thereby requested to drive the vehicle at increased speed for a short period of time in order that the required exhaust gas temperature can be reached for purposes of diesel particulate filter regeneration.

The fuel quality
It should be noted that the quality of the fuel must meet the DIN standard as stipulated in the instruction manual. Operation with biodiesel is not possible. The extended injection period for regeneration of the diesel particulate filter can lead to unburnt fuel on the cylinder wall entering the engine oil from the piston movement. Normal diesel fuel vaporises itself out of the oil in normal operating conditions. Biodiesel cannot do this effectively due to its higher boiling point. The oil is thinned as a result, which can lead to engine damage.

If the fuel contains a high level of sulphur, this can lead to impaired function of the particulate filter system with higher fuel consumption as a result of increased regeneration.
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post #20 of 93 Old 01-18-2019 Thread Starter
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Good to have all this info and insights. All up I think vw have built a better system than other brands inc Land Rover.
I hear some horror stories from mates owning Range Rovers, Discovery sport models.

Would be great to have a DPF visual indicator, which similar to other meters shows on screen what the soot levels are all the time and helps avoid a build up/limp mode situation.
If after 500kms of driving post lots of city driving will not trigger a regen to clear it up there should be an indicator to help avoid the situation.

Other question is, can the dpf be professionally cleaned to get rid of the ash so its renewed again?
Vw charge about $200 for a reburn at the dealership and will only replace the dpf once its full.
I hear of dpf specialist workshops that service the dpf - using different methods of cleaning, here’s an example.
https://www.dpfcleaning.com.au/
Such companies apparently charge about $600 to renew the dpf and bring it back to life.

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