Bimmerfest - BMW Forums - View Single Post - DPF soot rising very quickly prompting too frequent regens?
View Single Post
  #58  
Old 08-09-2017, 03:41 PM
AU Pete AU Pete is offline
Officially Welcomed to the 'Fest
Location: Sydney
 
Join Date: Jul 2015
Posts: 168
Mein Auto: 2007 X5 E70 3.0d
Hi all,

Just wanted to post an update - i have a theory about the Soot Mass "rising very quickly" and causing alarm.

Essentially, my theory is what Ard proposed back on page 1...

Quote:
Originally Posted by ard View Post
One possibility:
It may be the computer sets the value to 0 immediately after a regen, based on the assumption it has just been cleaned/emptied...but then, rapidly, as you drive the sensors (flow resistance, pressure differentials) become apparent and the computer then recalculates the soot load.

Which would mean it isnt creating massive amounts of soot and clogging, rather it is clogged and remains clogs- OR the sensors that are used to calculate the loads are somehow in error....
I've come to believe Ard is exactly right.
Here's why I believe that:

I monitored "Soot Mass" and "Simulated Soot Mass" simultaneously and charted the values.
If you just monitor these values while driving nothing weird jumps out.

When you chart the values, something very interesting appears.

They will display different values for a while, and then watch what happens when a regen starts...

Lets say you start with these parameters:
Soot Mass = 43gm, and Simulated Soot Mass = 36gm.
Then you notice a regen commencing (mine usually starts around 43gm-44gm soot mass).
The simulated soot mass number will begin dropping, and suddenly the "soot mass" value will jump to be an identical number to "simulated soot mass".

This is a key point.

The soot mass value has just shifted (i believe) from an actual reading (at least, a calculation of what it believes is the soot mass based on back pressure sensor values - i'm not saying theres a tiny set of scales in the DPF ), to a made up / simulated reading.

So the regen happens over the next 10 mins, your Soot Mass has dropped to somewhere between 0-15gm, and you think - 'Great! my DPF is now cleaned somewhat', but it hasn't, its still reflecting the "simulated soot mass" value - or the best case scenario. In practice, your DPF probably only burnt off a small amount of soot because its getting less and less efficient as it gets older. So in practice, lets assume over the period of that successful regen it just actually dropped from 43gm to 38gm. Again, you think it dropped to 0-15gm, because thats what the parameter said, but it didn't.

So then 3 minutes after your successful regen, the "Soot Mass" parameter switches back to a real reading (away from a simulated reading.)
It then begins climbing rapidly - because the computer is continuously recalculating the value based on pressure readings - and the distance travelled.
After 1 minute its displaying 20gm. Computer says "No - its still higher". Soot Mass keeps climbing.
After 3 minutes its displaying 30gm. Computer says "No - its still higher" Soot Mass keeps climbing.
It rapidly climbs up to 38gm and then stabilises, and begins climbing slower.
That's because its returned to its actual value it was physically able to regenerate to.
Then you've got a relatively short distance to travel before your soot mass climbs from 38gm to 43gm and the regen process has to start again.

Confirming - My belief is that a successful regen is only actually reducing the Soot Mass from 43gm to 38gm each time (in my case). And this is completely normal, and the best it can do given the remaining life of the DPF.


We think the forever rapidly climbing numbers are a problem, but its now my belief its just the computer recalculating the figures and shifting from a simulated value to a real value.

Here's my proof from charted values of simultaneously monitoring soot mass and simulated soot mass...





So, in summary - I think Ard was right on Page 1.
I think this is just what happens when your DPF is nearing full.
Normal operating behaviour, until it fills completely and can no longer do active regens, at which point you get it removed/cleaned, or replace it.
__________________
__________________
2007 E70 X5 3.0d

Last edited by AU Pete; 09-03-2017 at 02:38 PM.
Reply With Quote