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Does this apply to ISB 07 Cummins. How many miles does it take for that to develop?
Yes. O7 stands for 07 emissions which is the DPF system. Im not sure of a mileage, depends on the vehicle's route. Trucks that are stop and go, like in the city would plug up faster then a truck running long distances between stops. I clean mine every PMI. When they plug up you get the active code for EGR Diff pressure sensor, I think its a 411 code and normally an FMI 7.
If you see soot in the tailpipe it usually means the filter is cracked. It could run like this for a long time or shutdown. A simple crack could just allow soot to pass by, no big deal. Or the crack can continue to to get bigger eventually causing the filter to collapse causing low power or shutdown from exhaust restriction. Ive also pulled filters out and found no cracks or visible damage but had soot in the tailpipe. This usually means the soot is passing between the filter and metal casing. In any case there shouldn't be any soot at the tailpipe.