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VW MKV-A5 Golf/Jettas Discussions area for A5/MkV Jetta/Golf (2005/2006 PD and 2009 CR).

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Old February 13th, 2010, 11:03   #1
DoctorDawg
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Default Long-term DPF data project

The diesel particulate filter (DPF) is prolly the single most mis-understood and worry-inducing new feature of the '09-'10 CR engines. In an effort to bring more understanding to bear, I've started a long-term data collection effort using VCDS. Every day after my commute home (while the engine and exhaust system are still at full operating temp) I record the pressure differential across the DPF...the best available measure of the DPF's health (degree of obstruction)...while the tranny is in Park and revs are at 2000 (the pressure differential across the DPF is, of course, a function of engine revs, so if you want to measure yours you have to do it at some constant RPM; I've chosen 2000 RPM as my standard because exhaust pressure is reasonably high there, so you get good resolution). I also record daily several other parameters, such as distance driven since last regen, carbon mass, etc.
This project has been going for some 20 days now, so here's a peek at the early results:
I. PRESSURE DIFFERENTIAL AS A FUNCTION OF DISTANCE DRIVEN

This graph records the pressure differential across the DPF as a function of odometer miles (again, pressure is measured at full operating temperature, in Park, at 2000 RPM). Also, the vertical green and red lines record the odometer mileage at which each active regeneration event occurred (as determined from VCDS's "Distance driven since last regen" parameter). Green lines represent completed regens (i.e., not interrupted), and red lines represent interrupted regens (you can tell the difference because if you slow down from highway speeds or turn off your engine while a regen is in progress, your fans will run very loudly to cool down the DPF).
A few things to note in this graph:
1. Under my driving conditions (about 80% highway, 20% city), and with 34+K miles on my DPF, my pressures are running between 10 and 23 mbar (0.15 - 0.33 PSI). When the car was new, I recorded a few values as low as 5 mbar (0.07 PSI) (not shown), but I haven't been seeing any values that low in this data set, so its reasonable to conclude that over 34K miles I've accumulated a little bit of ash, but not much, as might be expected (and yes, I'm using 507.00 oil which I change myself, plus ULSD-compliant Stanadyne fuel additive). tdijoe tells me that the DPF idiot light comes on at 26 mbar. Employing a very rough back-of-the-envelope calculation, at my current apparent rate of ash accumulation (5 mbar per 34K miles) my DPF should hit the wall and always be at or above 26 mbar due to ash at around 140K miles. But please take this initial rough guesstimate with the very large grain of salt it currently deserves; I'll need to accumulate about 30K miles worth of data before I can accurately measure the upward trend in minimum pressure as a function of total miles driven.
2. Due to cold temperatures (which slow the time to full engine warm-up and normal EGT) plus some recent changes in my driving pattern, I've experienced four interrupted regens in a row. Please note that, nonetheless, the world as we know it has not come to an end. With my driving pattern (lots of highway miles) passive regeneration (not involving computer-controlled post-combustion fuel injections to super-heat the DPF) is doing a fine job of keeping my carbon load at a safe level, even without completed regens. Take-home: don't freak out if you interrupt a regen, or two, or several in a row. As long as you're doing a fair amount of highway driving, yer prolly fine.
3. As I've previously reported in other threads, regens typically happen about every 300 miles...but in this data set it ranges from about 250-375 miles. I'm sure the computer takes a lot of things into account when deciding when to launch a regen, but the parameter which seems to trump all others under normal conditions is simply distance driven since last regen. Note that the DPF pressure is not a triggering parameter (at least in the range of normal pressures shown here)...some of my regens happen when the pre-regen pressure is high, some happen when its low. Judging from the shorter-than-usual interval between regens 2 & 3 here (the first two red lines) if pressure is high and stays high for a sustained period then a regen is ordered rather earlier than 300 miles, which makes sense.
II. CARBON MASS
The ECU as viewed by VCDS reports two carbon accumulation parameters for the DPF: "carbon mass spec." and "carbon mass actual". The latter, on my car at least, is always zero...I don't believe this memory location is actually used (there are such things as carbon accumulation sensors, but the CR TDI's DPF doesn't have one; I think this parameter is currently just a place-holder so that if the VW engineers ever decide to add such a sensor to the DPF the software is ready for it). Carbon mass spec. however does change with time. I can't prove it, but I'm quite confident that this is a derived value, calculated from some model based on how much and what kind of driving you do. The next graph shows the relationship between this parameter's value (on the Y axis) and distance driven since last regen (on the X axis):

As you can see, the relationship is quite linear, with a pretty good correlation (r^2 = 0.93) but not a perfect correlation (perfect would be r^2 = 1.0). So the ECU appears to model carbon accumulation primarily based upon miles driven, but it also takes some other factors into account (probably things like speed, EGT, etc.).
Based on the data I've accumulated so far, carbon mass spec. appears to be a pretty worthless parameter. The next graph shows why I say this. It reports DPF pressure differential as a function of carbon mass spec. The dashed line is the linear least-squares fit to the data.

See what I mean? The measured reporter of DPF health, the pressure differential, bears no apparent relationship to the modeled parameter, carbon mass spec. When carbon mass spec. is low your DPF might be either breathing quite freely or rather obstructed, and the same is true when carbon mass spec is high. I have to admit I haven't a clue why the ECU is wasting its time tracking this apparently uninformative parameter.
III. A FEW MORE PARAMETERS, ALL OF THEM BORING
VCDS reports some other DPF-related parameters, none of which appear to be very useful. One is "Oil ash volume (mL)". This parameter has read "30" over the entire course of this data set. It will be interesting to see whether it increases after I change the oil and reset the service reminder. Another not-terribly-interesting parameter is "Requested regens". This parameter starts out at zero immediately after a regen, and then increases from zero to 1, then 1 to 2, then 2 to 3, then 3 to 4 over a few hundred miles. I've never seen it go higher than 4 before a regen happens. After a regen happens, it gets reset to zero. I think the name of this parameter, "Requested regens" is funky...one thing I know for sure is that it has nothing whatsoever to do with the number of regens requested by the ECU.
I'll post a new set of graphs to this thread after I've accumulated a few thousand more miles (and after the weather warms up, which will enable me to normally complete some regens). Stay tuned.
Readers who find this sort of terminally geeky stuff interesting may also enjoy some threads I posted regarding DPF data when my car was very new, including:
Invisible Smoke
FYI: DPF regen info from my '09 TDI
A Tale of Two Starts
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Last edited by DoctorDawg; February 13th, 2010 at 13:33.
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Old February 13th, 2010, 11:58   #2
UberVW_TDI
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Thank you for taking the time to post your DPF research. Interesting stuff. I've subscribed to your thread...
I wish VW would of included an indication light to let one know when the car is performing a regen. I've caught it mid-regen cycle 4 times now, which of course I didn't know until the fan kicks on after I shut the engine off. More information is better. Oh, and a turbo boost gauge would be fun to have too.
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Old February 14th, 2010, 06:23   #3
DoctorDawg
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P.S.: I encourage anyone else with an '09 or '10 who's as nerdy as I am, and who owns VCDS, to collect and occasionally post similar data. Right now, with N=1 (me), there's only so much one can conclude.

The most interesting insight that can come from these data will involve seeing how the minimum pressure differential increases with time. This should help us project how long a DPF will last in practice before getting ashed up and needing to be replaced, which is something I think a lot of people want to know. Different driving styles and patterns will affect DPF lifetime differently, so it would be useful to have this kind of data from a few different cars.
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Old February 14th, 2010, 07:24   #4
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Great data. Just a couple of questions / comments.

On the days where you had signifcant change in pressure (up or down), have you given any thought to what driving condition that day may have caused such a change? miles driven, speed different - possible higher/lower EGT resulting in better, poorer passive regens, higher / lower mpg resulting in lower / higher soot, and so forth

It would seem to me that if one wanted to get better baseline pressure values at various mileage points (say every 5 to 10k miles), that after a low daily pressure reading and especially after an interrupted regen (when the exhaust components are still very hot) that one could then go back out and drive in a lower gear (to increase EGT) for say 20 miles at higher speed so that more soot would be burned off and perhaps only ash remained. This might give a better estimate over time of remaining DPF life.

Also, what's your overall mpg through 35k miles?

Last edited by Plus 3 Golfer; March 3rd, 2010 at 06:23.
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Old February 14th, 2010, 08:05   #5
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Well, I know for sure that days on which the data show a significant decrease in pressure are days on which I was able to do a bit of spirited highway driving without getting stuck behind a slow-poke...nothing dramatic, just 65-70 MPH for maybe ten minutes. Days when pressure climbs a lot are the opposite...stuck behind a slow dump truck, or catching every dang red light. Passive regeneration is most effective at higher EGTs, which means higher revs.

My long-term MPGs are right around 45 in spring/summer/fall (all-time high was 50.6 on a 600 mile highway trip in great conditions), and drop to about 40 in winter.
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My other diesel gets 120 MPG (minutes per gallon): Kubota 2630 w/ FEL
My other other diesel I don't even want to talk about (1995 Dodge Ram 2500 Cummins 4x4)

Last edited by DoctorDawg; February 14th, 2010 at 08:57.
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Old February 14th, 2010, 09:18   #6
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Quote:
Originally Posted by DoctorDawg
P.S.: I encourage anyone else with an '09 or '10 who's as nerdy as I am, and who owns VCDS, to collect and occasionally post similar data. Right now, with N=1 (me), there's only so much one can conclude.
DrD, I'll gladly collect/post some of this data, since I just got my VCDS and Bentley, but am not very familiar with VCDS and all the tests one can do with it.
Would it be feasible for you to outline the steps required to get this data, i.e, which controller module, byte, bits, etc...one needs to access with VCDS to get this info, so as to allow other recent VCDS owners to gather this data?
Thanks in advance,
ML
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Old February 14th, 2010, 09:38   #7
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Here's a relationship that comes as a surprise to me. Thinking about which conditions are common to high-pressure days and which are common to low-pressure days, I decided to analyze my DPF pressure differential data as a function of the day's air temperature. In the graph below I'm using each day's average air temperature (courtesy of the National Weather Service). This seems reasonable because my morning commute happens at about the day's low temperature, and my afternoon commute happens at about the day's high temperature, so using the day's average temperature splits the difference.

Until I saw this graph I never would have guessed it, but it appears that lower pressure differentials across the DPF are observed on colder days (and, conversely, higher pressure differentials are observed on warmer days). The correlation is kinda weak...because a lot of other factors such as driving speed also influence the day's pressure differential...but it looks to my eye like there's a distinct relationship. More data needed here before I call this one, however, so stay tuned. I can't think how to explain this relationship, except that since colder air is more dense then maybe EGT (at any given engine load) is higher in cold air (due to more oxygen) than in warm air? And so passive regeneration is more efficient on colder days (at least once the engine reaches full operating temperature)? I dunno. Note that my commute is long enough (about 25 miles each way) that most of my driving time is spent at full operating temperature.
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My other other diesel I don't even want to talk about (1995 Dodge Ram 2500 Cummins 4x4)
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Old February 14th, 2010, 09:50   #8
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Very nice documentation; thanks!

Is it possible that some of the less "useful" data points the ECU is collecting are in anticipation of future smog testing requirements?

-dan
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Old February 14th, 2010, 10:03   #9
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Quote:
Originally Posted by funoutdoors121
Would it be feasible for you to outline the steps required to get this data, i.e, which controller module, byte, bits, etc...one needs to access with VCDS to get this info, so as to allow other recent VCDS owners to gather this data?
Happy to help. The following is true for VCDS Release 908.1 (the most recent version, last time I checked)...I can't speak for other versions.
1. Plug the cable into your car (lower left of dashboard) and computer.
2. Turn ignitiion to 'accessory' (the click between 'off' and 'start')
3. Launch VCDS
4. Click 'Select'
5. Click '01-Engine'
6. Click 'Adv. Meas. Values'
7. Select the values you want to monitor. Those which I find useful (with respect to the DPF) are:
099-1 Engine Speed
100-3 Particle Filter Differential Pressure
105-2 Requested Regenerations
106-3 Driven Distance Since Regeneration
108-2 Particle Filter Carbon Mass (spec)
Note that the units for 106-3 are kilometers, which don't work in my head, so I convert to miles. Having Engine Speed displayed helps me to nail 2000 RPM exactly when I'm measuring the differential pressure.

Knock yerself out!
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My other diesel gets 120 MPG (minutes per gallon): Kubota 2630 w/ FEL
My other other diesel I don't even want to talk about (1995 Dodge Ram 2500 Cummins 4x4)
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Old February 14th, 2010, 10:42   #10
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When I was playing with it, I found it interesting how much it cleaned itself out just going up a good grade (a few miles) on the freeway. Knocked the numbers right down. Make sure you're not driving when you are playing with it!
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Old February 14th, 2010, 13:33   #11
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DoctorDawd, thanks for VCDS info!
I'll experiment with all its options, using your post as a great starting point!
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Old February 14th, 2010, 14:25   #12
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Although I absolutely did not buy our CRD for the "Clean Diesel" aspect, I do find the science behind the technology worth scholarly review. Count me in as a subscriber to this thread and thanks for posting the quick and easy VCDS steps so I can get right in too! Our TDI is the wifes primary car, so my DPF study will be limited to weekend roadtrips riding shotgun.
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Old February 14th, 2010, 14:38   #13
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Quote:
Originally Posted by Osage Orange
Our TDI is the wifes primary car, so my DPF study will be limited to weekend roadtrips riding shotgun.
There's lots of fun things you can study with VCDS while the car is tooling down the road (hopefully driven by someone else), but do note that all the info I'm discussing here can (and should) be collected either in Park with the engine running (DPF differential pressure) or else with the engine off (all other parameters discussed here are accessible with engine off).

DPF-wise...as Turbine Suburban has already mentioned...it is interesting to watch highway driving under load melt away pressure-causing carbon build-up via passive regen.
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WeatherTech deflectors, Dieselgeek skid plate (both A+)
My other diesel gets 120 MPG (minutes per gallon): Kubota 2630 w/ FEL
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Old February 14th, 2010, 15:02   #14
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Quote:
Originally Posted by DoctorDawg
There's lots of fun things you can study with VCDS while the car is tooling down the road (hopefully driven by someone else), but do note that all the info I'm discussing here can (and should) be collected either in Park with the engine running (DPF differential pressure) or else with the engine off (all other parameters discussed here are accessible with engine off).

DPF-wise...as Turbine Suburban has already mentioned...it is interesting to watch highway driving under load melt away pressure-causing carbon build-up via passive regen.
Points noted, I just started playing with VCDS this weekend. I auto scanned, logged, and cleared an unrelated DTC already with it. So maybe I will be more help with these things understood, since a passive approach to this will also do.
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Old February 14th, 2010, 18:34   #15
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Quote:
Originally Posted by DoctorDawg
Happy to help. The following is true for VCDS Release 908.1 (the most recent version, last time I checked)...I can't speak for other versions.
1. Plug the cable into your car (lower left of dashboard) and computer.
2. Turn ignitiion to 'accessory' (the click between 'off' and 'start')
3. Launch VCDS
4. Click 'Select'
5. Click '01-Engine'
6. Click 'Adv. Meas. Values'
7. Select the values you want to monitor. Those which I find useful (with respect to the DPF) are:
099-1 Engine Speed
100-3 Particle Filter Differential Pressure
105-2 Requested Regenerations
106-3 Driven Distance Since Regeneration
108-2 Particle Filter Carbon Mass (spec)
Note that the units for 106-3 are kilometers, which don't work in my head, so I convert to miles. Having Engine Speed displayed helps me to nail 2000 RPM exactly when I'm measuring the differential pressure.

Knock yerself out!
For those with an 09 like mine the address are as follows: Thanks to Uwe

Quote:
First, note that the documentation in the dealers' own VAS-505x tools for this engine is very lacking. On our 2009 the groups where it claims the soot loads should be displayed are empty.

Instead, you will find this information in groups 240 and 241 (again, undocumented in the factory scan tool as of the latest brand CD).

240 gives you various information since the last regen:
240,2,Fuel consumption,since last regen,
240,3,Mileage,since last regen
240,4,Time elapsed,since Regeneration

and group 241 gives you the much sought after soot loads:
241,0,DPF Soot load
241,1,Particle Filter,Oil Ash Volume,Range: -380...+380 ml
241,2,soot load(g),calculated
241,3,soot load(g),measured

Note that field 1 has always been 0 for us.

As for the ECU regen behavior, in our experience it will want to start regenerating when either the calculated or the measured soot load hits 16-18 grams. The light doesn't come on the dash until a higher load which we think is 24g, but despite trying very hard, we've never been able to get it up to those levels. Other unverified information suggests that the ECU will also regen if no regen has happened during the last 750 to 1000km.

You can force a regen by going to the adaptation screen and selecting the appropriate option in the drop box; it will let you know which steps are necessary. Note that except in very special circumstances, forcing a regen is neither necessary nor desirable since it will decrease your fuel economy.

-Uwe-
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