It's probably time for me to produce some sort of reduction of all the info in that thread. It's not too difficult to get your head around it but I am aware now that I've used alternative terms for the same things in places. Apologies if that got confusing. I won't put any details here or back up what I'm saying with collected data, because all the data is in that thread and anyone can seek it.
Here goes !
The dpf captures excess soot particles from the exhaust gasses while the car is being used in town, and once out on the open road it burns off the soot to form harmless ash. That's the 'soundbite' description of what it does at least, but making it happen in such a simple way is far more difficult.
The soot is collected in the filter trap, which is made of the inert and robust silicon carbide, SiC (newer materials are coming along)
On the 2008 159 I have (some variations occur) the dpf is in the left of this casing, to the left of the temperature sensor dpf | Flickr - Photo Sharing!
To the right of the temperature sensor is the diesel oxidation catalyst, DOC which continues the job started upstream by the first catalyst, that is to reduce the levels of contemporary exhaust pollutants, for example NOx.
Most pollutants have been oxidised or reduced by the time the exhaust gasses reach the dpf and the soot which is left over is trapped in the dpf, to be disposed of later by the regeneration process
Regeneration of a dpf simply means raising the temperature high enough for the soot to burn in the remaining oxygen, to create ash, which blows through the filter and forms harmless microparticles.
3 types of regeneration
Passive, active and forced.
This is where through normal driving alone, the temperature of the dpf reches over 400 celsius (ballpark figure). At this temperature there is the possibility of passive and uncontrolled regeneration taking place and in theory, the filter can become unblocked completely if this process lasts long enough and occurs frequently enough
This is where the engine management uses tested parameters to establish the need for a dpf regeneration cycle. The parameters may include exhaust backpressure , time since last active regeneration and (in some cases, possibly not the Alfa 159) distance travelled.
An active regeneration is made to take place by the engine management system by firing the diesel fuel injectors during the exhaust cycle as the piston is rising in the cyclinder, and this squirt of diesel is mixed with those gasses in preparation for burning off completely later, as it travels through the exhaust and reaches the dpf.
This is where the extra fuel consumed during an active regeneration is used and where it goes. An active regeneration can last a varying amount of time (more data needed to find out how variable the time period of an active regeneration is), and presumably, the level of exhaust backpressure is measured after a regeneration to establish how much soot was burned off. (I think at this point that the pressure reading is considered to help calculate when the next regen occurs too)
This is just an active regeneration which is forced to take place by the owner/technician connecting to the car via a laptop and issuing a regeneration command. The car can be stationary, parked for this. High levels of heat are created in the exhaust underneath the car (and it's one reason why the exhaust tunnel is line with so many heat shields)
Blocked dpf ? What are the options ?
The blocked dpf is detected through the existence of excessive pressure in the dpf canister via the pressure sensor.
All of the following are valid actions...
- Remove the dpf and backwash it with water or soapy water (Youtube videos can be found showing this)
- Remap and dpf replaced with a bypass pipe
- Remap and dpf hollowed out
- Replace the dpf with a new one
- Drill holes in the existing one to bypass some pressure.
Each solution works. Washing the dpf is known to work with every dpf, but it is also known that it isn't a permanent fix. Removing and replacing the dpf with a bypass pipe also requires the removal of the DOC catalyst In the case of the earlier uncoupled dpf system). Hollowing out the dpf may or may not involve removing the DOC (depends how it's done)
It is a good idea to establish that the EGR system is functioning correctly, that the inlet manifold is clean and that you have at least an official Alfa EGR blocking plate (orifice plate) in the EGR circuit to reduce the effect of contamination from returned exhaust gasses as they flow through the air inlet system and manifold. A faulty EGR can cause excessive soot to be generated from the exhaust, which in turn blocks the filter, which causes the EGR to pass more sooty exhaust, etc....
Is doing nothing an option ?
Once you know that the dpf is blocked, either because of a dashboard warning or because you removed the dpf's temperature sensor and detected a lot of pressure manually, then I think it's time to weigh up the options.
Doing nothing about it causes problems for the engine. Besides significant fuel consumption, and loss of power and responsiveness (not to mention extra load on the turbo and it's bearings) contamination of the oil is also taking place at a fast rate
Additionally, the crankcase pressure also increases. Vital oil seals around rotating components, for example the crankshaft, keep the oil inside the engine under normal conditions. However, as crankcase pressure increases then oil can be passed by a worn oilseal. if it goes to the outside of the engine it is probably not going to be a problem. but if it manages to find it's way into the clutch bellhousing then the clutch will need to come out. (I'm not saying this has happened to an Alfa, only that it is known that high crankcase pressures will always increase the risk of seal failure)
What are the legal implications ?
Each of the above actions are workable solutions and are unlikely to cause an MOT failure.
I have an MOT due in December which involves a smoke test. I know the inlet is clean, the EGR works properly (and has the official orifice plate fitted) and by visual inspection alone there is no smoke at all after even just a few seconds of running from a cold start. I've run smokier cars which passed the MOT since the introduction of the advanced smoke test so I'm not concerned that I have introduced a reason for MOT failure at this point.
This is my dpf, the earlier uncoupled type which may be different to yours http://www.flickr.com/photos/2849605...in/photostream
on a 159 1.9JTDm (2008). Located roughly below the gearstick. it is suitable for drilling. Later model cars have the dpf closer to the exhaust manifold. I can't speak about that system from the point of view of personal experience. There may be information on the web by people who have already tried drilling it through. Initially it seems some sort of ECU defeating circuit needs to be added too.