Chaca Chaca Choo choo

[JimT]

Which engine? 871/2250/2350?

I'm gonna go out on a limb and guess that it's a 2250 or 2350 with SCR and that the stop engine light was due to SCR Inlet Temp too high???

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Edit:

Either way, with or without SCR, its likely the fuel being injected into the exhaust is not oxidizing properly in the DOC and burning later then it should or not burning fully. This could be due to a DOC that is no good, an exhaust leak screwing up the oxidation, maybe a clogged up or leaking DPF injector resulting in too much or too concentrated (bigger droplets instead of a mist) fuel in the exhaust. It could also be turbo or EGR related (causing excessive soot production), but I wouldn't jump to that conclusion until exploring other parts first...

Such as an EGR tuneup. When was the last time you went through the systems and cleaned things up/changed sensors? Might not be the direct cause, but will definitely be a factor in system performance.

Air filter? new, old, clogged up?

It's hard to say exactly what the cause may be. Could be a combination of things. Maybe start at the DPF injector and work your way back. Pop the injector off, make sure it isn't leaking and there isn't a wall of soot blocking it's spray pattern into the exhaust. --- If you DO find heavy soot buildup it's likely due to a leaky injector, a malfunctioning DPF Purge Air Actuator (contributing to a leaky injector) or burnt oily sooty exhaust collecting in there.