DoctorDawg
Veteran Member
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
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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