M925 Cummins ntc250 has a miss to it

[Olpa77]

I was out driving my M925 today and it developed a nasty miss fire. You can't really tell at idle but under throttle its really noticeable. A month or so ago I replaced all my fuel lines because I kept losing prime. Its holding prime now and I don't suspect I'm sucking air. Where should I start? Injectors? My truck does smoke quite a bit even at idle. Black smoke under power grey at idle and the smoke has that strong diesel smell.

 

[162tcat]

Have you adjusted your injectors? If not, start there and report back.

 

[VPed]

Mine has an NHC.

 

[162tcat]

Ok.....

 

[Floridianson]

Cumminns makes a product if you want to try it's called Flush and Adjust. Botom line you clean the injectors first then adjust. Wonder if adjusting does not clear the problem if you could get or have a Laser temp. gun and start it cold and take the temps of each exhaust port and see which injector is off hopeing it's just one?

 

[Coffey1]

OK for us non diesel mechanics how do you adjust them just so I will know in the future.

 

[Julian]

I have an M925 which also smokes too much and is low on power and I hope it is just an injector adjustment. They are actuated by the camshaft and adjusted like a head valve- you adjust a nut on the rocker arm that actuates the injector, but the procedure is very complicated for the first time. You should do the valves and the injectors at the same time. I have heard that some of the printed procedures are wrong. I think all M939 NHC250 engines use what is called "top stop" injectors and the adjustment procedure is different than the "non top stop" NHC250 injectors. There is loads of info both here and on the web about adjusting top-stop injectors. After reading about 15 different versions on how to do it, I think I am ready to try.

 

[VPed]

Here is a thread on the subject of setting the overhead: http://www.steelsoldiers.com/showthread.php?73256-Nhc250-valve-injector-overhead-adjusting

 

[Olpa77]

Thanks for the info. Yes it is a NHC not a NTC sorry about the typo. I will dive into it this weekend when I have some help and report back.