I have a number of rough spots that I have to avoid on our Nissan
ED33. None of them have what you describe as a misfire, but they will rattle the fillings out of your teeth.
Basically I am safe from 500 rpm to 1100, then I have to avoid 1100 to 1200, safe again to 1500, then shakes like heck till 1600, safe to around 1900 then shakes till 2000 then clears again to 2200 which is the most I have run it at, although the manual says it will do 2800, I have not had the guts to try it yet.
For what it is worth, I just had a hugely expensive rebuild
of the injector pump
and injectors (after feeding a lot of water
through the system) and although my wife reckons the motor is a bit smoother now, I can't feel much difference (except the thing starts) and it certainly did not affect the rough spots.
I am told by a diesel expert (not the armchair variety) that my engine is in excellent condition, and that these harmonics are to be expected due to hard mounting to the hull
, as in the truck it was on big rubber blocks to absorb all this stuff.
So in short, the roughness sounds ok but the misfire/cough worries me.