Lots or Regens and bad fuel milage

[JimT]

Need to see the aftertreatment history. Also, what is your oil and coolant consumption like? There can be many factors that lead to increased regens. You said you replaced the DPF, what about the DOC? If the only problem is the increased frequency and your aftertreatment numbers are good then you're probably just seeing the effects of age. If there are other symptoms then perhaps something else is the cause.

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For those that haven't had to deal with these systems or are not aware of how they work:

Passive Regen occurs normally while driving when the engine is under enough load that the exhaust temps are high enough to burn off some soot without the need to inject fuel via the doser. EGR might be used to help increase combustion temps.

Active Regen occurs when operating the vehicle and the soot load reaches a certain level. At this point extra heat is needed to burn off the soot, so the doser adds fuel to the exhaust. In addition to EGR, the turbo is also used to help increase the combustion temps. You will notice a slight increase in boost pressure during an active regen and sometimes a different sound from your turbo.

Parked Regen is similar to an Active Regen, except that while parked the engine is operated in a very consistent manor. This allows for the most efficient and effective baking of the soot as it doesn't have to deal with the ups and downs of normal driving conditions.

From what I've been told, on a fully healthy system with sufficiently high duty cycles, an Active regen should occur about once every 30 engine hours. On an older engine, or one that runs a lot of light duty cycles, then about every 8 engine hours is normal.

Running light loads or light duty cycles on the engine (like someone using little boost and getting really high fuel mileage) will result in more Active regens, as will an engine that produces more soot or other particles that get caught in the filter. A faulty EGR valve or bad sensor or blockage can result in combustion temps that are too low for a Passive regen. Same goes for turbo problems. Low combustion temps will also affect Active Regens. Sometimes resulting in white smoke before the temps get high enough.

Higher oil consumption will also lead to problems. Not only can it clog up the DPF faster, but the oil can either clog up the face of the DOC or it can build up a coating inside the DOC's surfaces limiting the oxidation of the exhaust gases. This also leads to white smoke and long regens that struggle to get above about 750F. (learned this one from recent experience, DOC coated but not plugged, leading to a lack of oxidation causing fuel to ignite later in the system, only partially or not at all. In my case it left a nice film all over my rear frame and trailer)

Then there's exhaust leaks. These usually affect the different pressure readings that the ECM uses to calculate soot load and exhaust restriction. Depending where the leak is it can also affect the location and the way the added fuel burns in the aftertreatment system.

Then there's the SCR system. With a structure similar to that of the DOC it can also clog up, especially since it expects relatively clean exhaust coming out of the DPF. Any unburnt residue can coat it's surfaces and cause restrictions and NOx conversion problems. There's also the tendency for the DEF to build up and create blockages or restrictions. A DEF doser valve that allows too much DEf to enter the system can cause this. The resulting pressure increase can also lead to more frequent regens. The DEF itself is supposed to burn or melt at relatively low temps so restrictions due to buildup can come and go. Another problem is that faulty NOx sensors or bad catalyst conversion rates can lead to SCR faults that sometimes disable EGR, which in turn screws up the balance of the entire system.

As Rawze likes to point out, these systems barely function correctly when everything is in perfect condition. But once even one tiny thing gets out of whack it can cause a myriad of problems that are difficult to troubleshoot.