Leoflavio
10-05-2010, 12:33 PM
Its appears that DFP Blockages or problems aren't as simple as swapping out the old pdf and replacing with new - though that in itself can be a somewhat costly adventure.
Having scanned across the web and read as much as I can, I arrive at the following opinion. There's a heck of a lot of very poor guessing going on out there. So in the interests of getting my issue solved as well as providing a means for others to gather slightly more sensible advice - here goes.
Different engine types will use different DPF systems. This is an important thing to bear in mind. Some, like the newer Touaregs and Passats (and related marque derivatives) use an additive tank as part of the regeneration process. I'm not focusing on those as my system doesn't do that. However, I figure that much of what I have gleaned may be useful to understanding more about your own DPF.
The 3.0 V6 TDI Engine BMK is a bit older now and will be found on Audi A6's, possibly early Touaregs etc.
This engine doesn't use exhaust additives and works as follows: Looking at the exhaust system from under the car, you'll see nearest the engine a large bulbous section. This is a Cat. Removal thereof will be a major mission. Don't do it just because you think that it follows that the DPF will be nearest the Turbo. The second section (sort of under the 2 front seats) is the DPF. The removal thereof is fairly straight forward. 3 nuts at the head get undone. Then a bracket that links it to the rear of the ehaust (going to the twin silencer boxes) gets undone. Disconnect the 2 hoses that connect to the pipes (Pressure Sensor stuff). Should be about 10 minutes in total.
HINT: If in doubt about which is the DPF. Check for pipes that lead away from it fore and aft. These pipes connect to the Exhaust Pressure Sensor. An integral part of the car's management system, telling it when it thinks the filter needs regeneration by measuring differences in exhaust pressure BEFORE the filter and AFTER the filter.
So how does this regeneration process work? Well, the car uses 2 different processes. PASSIVE Regeneration: This occurs while you drive. When exhaust heat is great enough, it allows the platinum catylist in the DPF to start a regeneration process. The car will read the pressure before and aft the DPF and know that all is well with the world. ACTIVE regeneration: Driving styles or short journeys may not allow the exhaust temp to get hot enough to automatically start the Regen Process. In this case, the car will read, via pressure sensors, that the DPF is getting fuller. At a preset level (set at factory) the car will switch to ACTIVE regeneration. This should be a seamless process where the car will modify its fuel burn behaviour to compensate for possible power loss during the Regen. Additional fuel will be pumped in, leaving some unburnt which can gather on the face of the DPF (or something along those lines). The various other Exhaust Emissions Systems will also play a part to modify and moderate the flow of air, exhaust recirculation shut down or increase etc in order to get the active regen going.
Did you spot that potential problem area? The entire Exhaust Emissions Systems play a part in the active regeneration process. I suspect that if one or some of the components of the system, as a whole, are out of kilter that ACTIVE regeneration will not occur after an extended period. The car may continue to do so on a miles or time based assumption, but this is not an accurate thing and may allow for the clogging up of the DPF. After all the car is running blind cos it can't actually measure what's what (if the sensors and feedback mechanisms aren't perfect and within behaviour parameters) and may probably get it wrong eventually.
So, the very first thing to consider are the fault codes. Especially anything that has bearing on causes of car Asthma - ie: how the car breathes. As an aside, you know how irritating it can be to have an Exhaust Workshop light go on and then struggle to get it off again, especially if you've taken the car into a dealer and all they want to do is replace expensive parts until the light goes off, which seems like a step too far because you have other financial concerns like paying the mortgage? I'm afraid I'm not the bearer of good news then - if you want longevity from your diesel, best to ensure it can breathe well.
So, starting at the air intake, you'll find air filters, Air Mass sensor, Throttle valve, Inlet manifold flaps attached to motors, Exhaust gas recirculating valves etc and various and assorted sensors reading temp and flow. Of course, blocked fuel filters can also add to the joy as the car needs to modify fuel delivery to create active regeneration.
Why do all these things exist? Legislation! Cars are obliged to create less mess, hence the increasing complexity of emissions systems. I suspect, though I have no real substantiated idea, that bypassing any of the cars systems will create a fault code and break the required feedback loop the car needs to enter the active process.
Lastly, it can be that everything is running tickity boo, but still the DPF doesn't want to play well with others. Well, the DPF is exactly that, a filter. Filters eventually need replacing as they get clogged up. The regeneration process can ONLY burn the soot. What it can't do is remove the residue ash from the filter that is created after the clean. In time the ash buildup will simply be too great to allow sufficient air flow through, meaning a replacement.
The DPF is build differently to a Cat. If you look through a CAT, assuming you have a straight line from front to back. You'll notice a honeycomb of sorts of fine passages that free flow from front to back. The DPF uses a honey comb design (DPF filters are of different designs and use different technologies and materials), but alternate channels are either open of blocked. This means that air flows in to an open channel with blocked end and is forced to move up or down to another channel that has its back end open. This traps the soot, allowing regen to reduce it to trapped ash.
Oh yes, I do have a question as well. Who'd have thought after all that blurb! If replacing the DPF, does the car need to be reset to KNOW that it is definitively starting with a 0% ash content filter? And if so, can anyone explain in more detail using VAG COM or so.
If anyone would like to amend what I've said, I'm all ears please. Best we ensure that correct info is being circulated among the community.
Best Regards to all.
Added on Edit: From a maintenance perspective I thought I'd add this as well. Engine Oil spec. Like everything else with modern Diesels, the right engine oil is critical to ensuring decent longlife performance. Reason for this is that the correct engine oil is designed to lower soot output into the exhaust, further helping your expensive DPF to live longer. Diesels have lots of piston blowby and therefore some of the combustion ends up mixing in the engine oil. Correct oil traps this and reduces exhaust load on the DPF. Seems like a good case for more regular oil changes as well then.
Having scanned across the web and read as much as I can, I arrive at the following opinion. There's a heck of a lot of very poor guessing going on out there. So in the interests of getting my issue solved as well as providing a means for others to gather slightly more sensible advice - here goes.
Different engine types will use different DPF systems. This is an important thing to bear in mind. Some, like the newer Touaregs and Passats (and related marque derivatives) use an additive tank as part of the regeneration process. I'm not focusing on those as my system doesn't do that. However, I figure that much of what I have gleaned may be useful to understanding more about your own DPF.
The 3.0 V6 TDI Engine BMK is a bit older now and will be found on Audi A6's, possibly early Touaregs etc.
This engine doesn't use exhaust additives and works as follows: Looking at the exhaust system from under the car, you'll see nearest the engine a large bulbous section. This is a Cat. Removal thereof will be a major mission. Don't do it just because you think that it follows that the DPF will be nearest the Turbo. The second section (sort of under the 2 front seats) is the DPF. The removal thereof is fairly straight forward. 3 nuts at the head get undone. Then a bracket that links it to the rear of the ehaust (going to the twin silencer boxes) gets undone. Disconnect the 2 hoses that connect to the pipes (Pressure Sensor stuff). Should be about 10 minutes in total.
HINT: If in doubt about which is the DPF. Check for pipes that lead away from it fore and aft. These pipes connect to the Exhaust Pressure Sensor. An integral part of the car's management system, telling it when it thinks the filter needs regeneration by measuring differences in exhaust pressure BEFORE the filter and AFTER the filter.
So how does this regeneration process work? Well, the car uses 2 different processes. PASSIVE Regeneration: This occurs while you drive. When exhaust heat is great enough, it allows the platinum catylist in the DPF to start a regeneration process. The car will read the pressure before and aft the DPF and know that all is well with the world. ACTIVE regeneration: Driving styles or short journeys may not allow the exhaust temp to get hot enough to automatically start the Regen Process. In this case, the car will read, via pressure sensors, that the DPF is getting fuller. At a preset level (set at factory) the car will switch to ACTIVE regeneration. This should be a seamless process where the car will modify its fuel burn behaviour to compensate for possible power loss during the Regen. Additional fuel will be pumped in, leaving some unburnt which can gather on the face of the DPF (or something along those lines). The various other Exhaust Emissions Systems will also play a part to modify and moderate the flow of air, exhaust recirculation shut down or increase etc in order to get the active regen going.
Did you spot that potential problem area? The entire Exhaust Emissions Systems play a part in the active regeneration process. I suspect that if one or some of the components of the system, as a whole, are out of kilter that ACTIVE regeneration will not occur after an extended period. The car may continue to do so on a miles or time based assumption, but this is not an accurate thing and may allow for the clogging up of the DPF. After all the car is running blind cos it can't actually measure what's what (if the sensors and feedback mechanisms aren't perfect and within behaviour parameters) and may probably get it wrong eventually.
So, the very first thing to consider are the fault codes. Especially anything that has bearing on causes of car Asthma - ie: how the car breathes. As an aside, you know how irritating it can be to have an Exhaust Workshop light go on and then struggle to get it off again, especially if you've taken the car into a dealer and all they want to do is replace expensive parts until the light goes off, which seems like a step too far because you have other financial concerns like paying the mortgage? I'm afraid I'm not the bearer of good news then - if you want longevity from your diesel, best to ensure it can breathe well.
So, starting at the air intake, you'll find air filters, Air Mass sensor, Throttle valve, Inlet manifold flaps attached to motors, Exhaust gas recirculating valves etc and various and assorted sensors reading temp and flow. Of course, blocked fuel filters can also add to the joy as the car needs to modify fuel delivery to create active regeneration.
Why do all these things exist? Legislation! Cars are obliged to create less mess, hence the increasing complexity of emissions systems. I suspect, though I have no real substantiated idea, that bypassing any of the cars systems will create a fault code and break the required feedback loop the car needs to enter the active process.
Lastly, it can be that everything is running tickity boo, but still the DPF doesn't want to play well with others. Well, the DPF is exactly that, a filter. Filters eventually need replacing as they get clogged up. The regeneration process can ONLY burn the soot. What it can't do is remove the residue ash from the filter that is created after the clean. In time the ash buildup will simply be too great to allow sufficient air flow through, meaning a replacement.
The DPF is build differently to a Cat. If you look through a CAT, assuming you have a straight line from front to back. You'll notice a honeycomb of sorts of fine passages that free flow from front to back. The DPF uses a honey comb design (DPF filters are of different designs and use different technologies and materials), but alternate channels are either open of blocked. This means that air flows in to an open channel with blocked end and is forced to move up or down to another channel that has its back end open. This traps the soot, allowing regen to reduce it to trapped ash.
Oh yes, I do have a question as well. Who'd have thought after all that blurb! If replacing the DPF, does the car need to be reset to KNOW that it is definitively starting with a 0% ash content filter? And if so, can anyone explain in more detail using VAG COM or so.
If anyone would like to amend what I've said, I'm all ears please. Best we ensure that correct info is being circulated among the community.
Best Regards to all.
Added on Edit: From a maintenance perspective I thought I'd add this as well. Engine Oil spec. Like everything else with modern Diesels, the right engine oil is critical to ensuring decent longlife performance. Reason for this is that the correct engine oil is designed to lower soot output into the exhaust, further helping your expensive DPF to live longer. Diesels have lots of piston blowby and therefore some of the combustion ends up mixing in the engine oil. Correct oil traps this and reduces exhaust load on the DPF. Seems like a good case for more regular oil changes as well then.