M931 Not running right aftert parade

[Bowtie70SS]

My neighbor has a M931 (I think) and it is not running right. We did a local homecoming parade last week and his truck started to run bad on the way home. He was idling in traffic and said he heard the engine sound change. He went to take off and the truck chugged and black smoked. He made it home and called me to check it out. I have a deuce and also have a pretty extensive mechanical backround on gasoline stuff. I checked the easy stuff and ended up changing filters and draining some fuel. It seems to run a little better but it is obviously only running on 4 or 5 cylinders. It is smoking at idle like raw fuel smoke. It has a noise in the engine but it seems to be from the middle or top. I was told that insufficent pump pressure, a bad injector, or a bad head gasket could be the cause. I came up with the idea of a bad rocker arm or push rod but have not pulled the valve cover yet. Where do I start? I dont have any diesel tools but am very mechanically capable. I would like to do some preliminary tests before just telling him to take it somewhere.

 

[162tcat]

Which engine?

 

[Suprman]

I had a Cummins 250 that ran like that low power smoke and you could hear the miss it would send backpressure into the intake stack. One of the rocker arms had slipped off. I thought it was very strange but if it can happen once then it can happen again.
Will

 

[swbradley1]

What color is the smoke?

Does the smoke have any peculiar smell to it other than normal diesel?

 

[Bowtie70SS]

Its is the Cummins 250, the smoke looks like normal diesel smoke gray-ish as in unburnt fuel. Would a short video help? I'm really trying to help the guy out before he takes it to have it worked on. To me it is weird that it happened so suddenly, that's what made me think valve train.

 

[162tcat]

Adjust valves and injectors first. That's the best place to start.

 

[Bowtie70SS]

I just went out and pulled valve cover. 1 intake valve was probably 75% backed off they all need adjusted. I was working alone so I did not check them all and it is a pain to jump down and bump engine over. Any of you gurus know where in the TM the specs/procedure are? I assume -20 ?

 

[dmetalmiki]

crack each injector seperately and see if the smoke fades. and do the above also.

 

[162tcat]

Read the pinned topic on this at the top of the forum. It's "NHC-250 valve and injector adjustment" or something like that.

 

[Bowtie70SS]

All right I screwed up , it is a M923A2 with a Cummins 6cta. Where are valve lash specs? .012 and .024? Intake and exhaust.

 

[Bowtie70SS]

All right I screwed up , it is a M923A2 with a Cummins 6cta. Where are valve lash specs? .012 and .024? Intake and exhaust.

Ok I adjusted the valves yesterday and we started it again it does run lots better but there is still a issue . It sounds like there is a miss and when I cracked the injectors the same cylinder that had the rocker backed off appears to not affect the idle speed when I crack the injector. I believe that number 2 injector could be bad but there is a definite and knock its relatively loud heard that noise be caused by a bad injector or am I looking at taking the head off and/or dropping the pan to remove the piston?

 

[74M35A2]

Swap the #2 injector with one of another cylinder and see if the problem follows the injector. If it does, then you know where the problem is (injector).

Is you "neighbor" not on this board?

 

[Bowtie70SS]

Nope, he is not. He doesn't even have the internet, I am the tech support. In these situations you not only need the internet but the capability to do the work. I went to school with my neighbor and I have known him and his dad for 20 years. Swapping the injectors is a great idea and I will do that. Thanks