NMF cleans your engine and suspends the residue in the oil to be removed by the filter. Cummins ISX engines run dirty, so at the point that you first apply NMF, your system may already have much residue in it. During the first application of NMF, enough residue may be cleaned away to clog your oil filter. If your oil pressure drops significantly, that is probably what has happened. For this reason, during your initial treatment of NMF, please have a couple oil filters handy in case you need to change out filters.
