Originally Posted by vloney

If a DPF is cracked sufficiently to have sooty pipes, the "hole" will be significant.

Originally Posted by SpartanDieselTech

There are only 2 things that ultimately contribute to fueling- injection pressure and injection pulsewidth (added up over the multiple injection shots). The diagnostics that control the pump are pretty *tight*, ie it doesn't take significant error to throw codes. Any difference enough to add up to an overfueling condition from either the pressure or volume control valve will throw the truck into limp and DTC's long before any DPF damage comes about.

It only takes a small crack in the DPF to allow soot by; even a very tiny amount will build up soot in the pipes and not much more to see visible smoke. These engines run low injection timing (and correspondingly more particulates) in order to keep NOX emissions down; the exhaust in the downpipe contains a visible amount of soot the majority of the time under load.

The calibrated error thresholds for the DPF pressure sensor to detect an actual leak aren't as stringent as one might think, simply because there are fluctuations in average pressure over the lifepsan of the DPF and simply in the allowed tolerances as the DPF's are manufactured. The tolerances allowed would not detect the small leaks that are necessary to build up soot or visible smoke.

If it gets bad enough, obviously, codes will be thrown and limp mode will likely ensue, but not all the time. Most DPF cracks happen diagonally across the substrate filter media between the "squares" inside or down the length of the ceramic mesh that binds the substrate squares together. Given the average volume of exhaust passing through the DPF at any given point in time, it takes a pretty hefty leak to cause a detectable amount of pressure drop- let alone one large enough to exceed the calibrated thresholds. The tolerances are more than enough to allow soot buildup and smoking if the DPF contains small cracks.

I can also definitively tell you from looking at the calibration that fueling is in no way directly controlled by the DPF pressure sensor; even for the POST2 "regen" injection. The pressure sensor can request small percentage changes in fueling based on large differentials but normal fueling functions are controlled simply by mass fueling tables.

As for the EGRTB sensor, it being out of calibration could allow the EGR valve to open farther and for longer than needed, decreasing oxygen to the cylinders and increasing particulate production- this would increase overall catalyst and DPF temperatures on average and affect lifespan over time, but once again there are error thresholds for how much duty cycle change is allowed based on EGR inlet/exit temperature differentials. As for coolant quality- anything that affects the function of the EGR coolers- be it air bubbles from low coolant level or whatever else will affect the efficiency of the coolers and provide less temperature drop in the incoming exhaust to the intake manifold. This could also affect soot production as high EGR temperatures require more EGR flow in order to do the same job (and the calibration is aware of this). However, just like the last scenario, there are numerous plausibility diagnostics in place to ensure that these tolerances don't pile up on each other to create a condition that shortens the lifespan of any of the components or cause a drivability concern.

No DPF can allow soot to leak by because it is "overwhelmed" or the presence to too much soot. It can only leak by physical failure; ie cracking; which can be accelerated by too much soot or regens that are too hot or too long due to a malfunction. I see this myth float around the forums a lot.

To answer vloney's question directly, yes, there are situations with hardware control such as the pump valves that can accelerate failure of the DPF under the right conditions. However, I firmly believe none of the conditions could occur in a situation without tripping the diagnostics and correspondingly causing the truck to run like absolute ***. DPF's that so happen to fail and leak soot without diagnostic warning or indications were, IMO, simply faulty components to start with. They are prone to failure inherently by current design.

Originally Posted by JohnD333

DPF was not replaced. Everything factory stock. I did not wash/clean exhaust pipes. After 2k miles of highway heavy (5th wheel w 25k combined weight on a 450 w/4.3 gears), with regen every 80-100 miles like clockwork, my exhaust pipes are clean again. Sure glad they fixed the source of the black.