I have a 1996 12V with 170,000 miles on it. This past winter, it didn't start as easily as past winters. Have synthetic Rotella 5W-40 and cranking speed was not a problem! But it didn't fire as snappily as before, and when it did run, it ran rough with a lot of smoke. Pretty sure the manifold heater worked and I was using winterized fuel.
I suspect that maybe the injector nozzles might not be performing optimally, but I have talked to a couple of Cummins/Dodge dealers and can find nobody that will say "you ought to consider at least inspecting the nozzles".
Anybody out there had to replace nozzles at or before 170K miles?

 

I wouldn't go so far as thinking you need to replace them , but pull the injectors out , and have them tested , for pop pressure , and get them to look at the spray pattern, it is possible they just need a good cleaning.

 

Sounds more like the timing slipped a bit. Might be good to start there.

I was told my the local injection shop that around 150k is when injectors may start to need attention. At least by that time they aren't as optimal as new. It's not so much the tips as some of the internal parts such as springs that deteriorate and popoff pressures drop out of spec.

Vaughn