The trucks are only so smart. I mean chances are if theres no code like i had its a plug gone bad. My bet is a code will only show if it is a bad cop. The ecm/pcm would know that via electronics. Think about it cop is good, it knows that, but engine stumbles anyway. How else would the truck know it has a missfire?? Prob would need to know contribution % via the crank sensor maybe, and i doubt these trucks can do that. I think ppl assume vehicles now a days are super smart, but there still are hard parts in the engine that can fail.
From the cummins side, the ecm can determine misfire via cylinder contribution from the crank sensor. Its kinda nice lol. As bad as my truck was running i SHOULD have had a code, so thats when i was shure it was a bad plug when i had this issue, and it was. I unplugged one injector at a time till i found the dud cylinder..The rpm tach on the edge helped too...
SORRY for getting off topic