Excessive smoke out of the NHC 250

I just read that forum and yes it does help! Hopefully some adjustment will cure all my problems!

Well I went to adjust the injectors last night using the method described in the Nhc250 valve injector overhead adjusting thread. Once I rolled the motor over so that the pointer aligned with 1-6 VS on the pulley I found that the number 1 injector rocker was not down into the injector. So I came to the conclusion that the accessory drive pulley might be out of time so I decided to use a dial indicator to find out when the injector is being pushed all the way down. After I found when the injector rocker was on the very top of the cam lobe I looked at the accessory drive pulley to see how far off the mark was. The mark was nowhere to be seen. So I continued to adjust all injectors using the dial indicator as a reference. Just like that there was hardly any smoke coming out of the exhaust. So my guess is someone adjusted the injectors using the marks on the pulley ( which is way off)!!! Is there a key way in the accessory drive pulley or is it just pressed on??

Glad to hear that you got the old girl up and running smoother.

looks like a pin is in the shaft, the pully has a key way that alines with the pin
tm9-2320-260-34-1, 3.8 covers this

If the A or VS1-6 is at the pointer and the injector on 1 or 6 isn't all the way down the acc dr. is out of time or it isn't adjusted right. Only way to fix the acc dr is to pull it out and re install it correctly. You can do the overhead with it out of time though.

Sounds like you are on the right track with checking the overhead. Starts good, whithe smoke at idle and black smoke when loaded.

If you need help, PM me.

I verified the acc drive marks using the dial indicator on #5 injector. as #5 just starts moving; that should be 1-6VS and can be marked as such in the event the acc. drive is on wrong or slipped. used dial indicator because turning the engine by hand is too slow to really watch #5.
if its not, spin the acc. drive another 360 and check again.

Either way when both rockers are loose for a given cylinder, that injector should be closed fully.

Now when you say "Either way when both rockers are loose for a given cylinder, that injector should be closed fully" do you mean the injector is pushed all the way down? Is the injector considered to be open when the rocker is not pushing down on it and then closed when it is pushed down? I'm not quite sure how the injector works, because to me it would seem the injector is open when it is pushed down.

smittyjr355 said:

Now when you say "Either way when both rockers are loose for a given cylinder, that injector should be closed fully" do you mean the injector is pushed all the way down? Is the injector considered to be open when the rocker is not pushing down on it and then closed when it is pushed down? I'm not quite sure how the injector works, because to me it would seem the injector is open when it is pushed down.

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Yes. Down is closed, up is open.

The camshaft holds the injector closed until it needs fuel, then the camshaft allows it to open briefly, then closes it back. What the rocker is pushing down is a pin (plunger) that seals the injector closed.

It should also be said that the pin (plunger) goes with the injector. Do not mix the pins (plungers) and injectors up.

smittyjr355 said:

Now when you say "Either way when both rockers are loose for a given cylinder, that injector should be closed fully" do you mean the injector is pushed all the way down? Is the injector considered to be open when the rocker is not pushing down on it and then closed when it is pushed down? I'm not quite sure how the injector works, because to me it would seem the injector is open when it is pushed down.

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Yep, what mkee said! remember this is a direct injection engine, so when the cylinder is in the firing position (valves closed) that injector MUST be closed or combustion pressure will enter the fuel injector and fuel rail?? wreaking havoc and making it run rough and smoke a lot {ask me how I know}. Kinda counter-intuative with the injector rocker being pushed for us gasoline guys.

i have a 1984250nhc cummins, upon start and driving little to no smoke at all, very slow throttle response , small hills barely 1500 rpm and down shifting .Help?????

Maybe fuel or air starvation

hank2424 said:

i have a 1984250nhc cummins, upon start and driving little to no smoke at all, very slow throttle response , small hills barely 1500 rpm and down shifting .Help?????

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Upon initial start up does it crank for a while or does it fire right up?

I bought a 71 m818 and mine smokes white when started then seems to clear up until you give it throttle them out smokes whiteish grey and smells like oil... The trucks been sitting for years so not sure which direction to go. Stuck injector, bad head gasket or valve guides... Any suggestions?

Could be incorrect heads or worn out. Injector issues will not smell of oil.

WillWagner said:

Could be incorrect heads or worn out. Injector issues will not smell of oil.

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Could it be someone poured oil in the fuel to lube the injection system after sitting for years and poured too much for the amount of fuel they put in it?

Screamindemon said:

Could it be someone poured oil in the fuel to lube the injection system after sitting for years and poured too much for the amount of fuel they put in it?

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Here is a video of the truck

Look at the fuel in the tank, should be clear/light colored. If it is dark, maybe oil in the fuel, red tint, ATF. How cold is it there? NHC will smoke white when very cold, Idling/not working the NHC is like the LDT, they will smoke and smell of oil if not worked. The engine sounds good though. The valve cover that has the filler cap on it looks wet. An easy way to find out if it is totally worn out is to remove the filler cap. When it is removed, if the cap feels like it wants to blow off of the cover, most likely worn out. The cap should be able to be loosened and it will sit on the filler hole and just dance around. Another thing is that if the blow-by tube is blocked, pressure will find the easiest path out, usually the filler cap, valve cover gaskets, front or rear main.....yes, the engine makes pressure in the crankcase, totally normal....look at the blow-by tube and feel it. slight pressure is normal, lots of air, worn out, nothing and the cap wants to blow out of your hand, it is blocked.

Head gasket won't cause oil burning, stuck injector will miss. Incorrect tune up will cause the smoke, but it smells of fuel. Guides, maybe, no seals on these, like I said, idle time is an issue on them and oil will migrate down the guides

I lied about the heads. If it is NA, the plug needs to be out of the head, turbocharged, blocked. CRS syndrome

Cummins developed a 'smoke kit' for the NHC-250 . The 'kit' was a turbo and associated parts. It served the same purpose as the smoke kit used on the 2-1/2 ton LD-465 Multi-fuel. The link below has more information. The problems mentioned here (so far) sound like part failures or adjustment issues. The 'smoke kit' is not a solution to these problems. I am adding the link (to a link) here as it may be of interest to others who make it here and want to reduce smoke (and/ or increasing power) on properly running engines.