Cummins X15 after treatment issues

[JimT]

Well, I had a reply with some of the same stuff as Rawze, so instead of repeating I'll just add a couple things.

Many people overlook the role of the SCR components/system. A lot of that turbo spooling you say is regen related, it's actually more likely the warmup/keep warm function of the SCR system. Especially when you hear it kick in when sitting idle of traffic lights during stop and go city driving. It does this to keep the SCR temp high enough to allow more efficient NOx conversion. If the outlet NOx sensor is faulty or just reading higher then targeted NOx emissions or maybe the SCR temp sensor, then the ECM will adjust operation of the engine/turbo and EGR to compensate. Blockages or DEF buildup in the SCR system can also cause exhaust restriction issues further up the line in the DPF/DOC, the turbo and of course the engine itself.

One of the most important things to learn is that ALL of these systems need to function 100% correctly and work together by sending data back to the ECM which will adjust various aspects of operation.

A lot of the modern engine operation is dictated not by soot and DPF operation but instead by stricter and stricter NOx emission standards. The DOC/DPF and soot collection requirements really haven't changed much since their introduction, other than maybe shrinking in size and increased operational efficiency. I mention this because many of the design and operational choices for these newer engines reflect the NOx emissions requirements. The push for lower RPM engine operation is bad for engine longevity, but helps reduce NOx production (and the manufacturers don't care, it helps them hit the government targets and they just get to sell you more parts and engines as a result). But lower RPM operation (more torque, less HP) also tends to yield more soot, therefore more work for the DPF. --- Now add taller gear ratios and drivers that have been brainwashed (or actually forced due to RPM limiters) to lug the engine and you get faster engine wear. That engine wear leads to increased oil consumption, which adds even more soot to the exhaust.

The point here is that due to stricter emissions standards the systems are hyper sensitive and are constantly adjusting to try to stay in balance, even shiny new from the factory. But they can only react to the data they have and with the programming built into the ECM. You can't ignore warning signs, such as the MIL coming on (especially not for 6-12 months!). You also need to be proactive to ensure optimal operation of the entire system, both mechanically and electronically. You also need to train your drivers on the best way to operate these trucks, otherwise their driving habits will be at odds with the ECM's attempted operation and will directly contribute to repeated breakdowns.

Oh, and don't buy into that extended oil drain crap. Having a worn camshaft at 270k mi is directly related to excessive soot buildup in the oil. A bypass oil filter will help reduce the soot, but the oil itself breaks down over time and loses it's helpful additives. You need to stay with normal drain intervals, 8-15k miles, dependent on fuel mileage.