service manual to replace injectors in 1972 Cummins VT8-370-M engines


   Noticed last season for first time in 6 years of ownership, a bit of black smoke from both of Fire Escapes exhaust. Fire Escape is my 1972 470 Commander. Came from factory and ultimately to me equipped with VT8-370-M Cummins diesels and have been very satisfied with condition and performance. 

Have received advice it may be time to service injectors. Have been a gasser before this and been getting educated inch by inch on my old diesels. Is there a shop manual or on line site to bring me up to speed on this next education ?

Thanx and I am grateful for the forum and any help offered.

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Check the library files section

Engines - Diesel  there is some info on VT 8-370's there.

   Thank you

Charlene Pike said:

Check the library files section

Engines - Diesel  there is some info on VT 8-370's there.

Did the black smoke happen when you were increasing the throttle setting, and did it go away after a minute or two?


Thank you for your interest in assisting.

I have maintained fuel filters regularly and am certain of the fuel quality. I have not yet observed the build up of soot on transom which I have noted on some other older diesel boats in my area. I do not intend to allow that condition on my old beauty. 

The smoke is heavier when starting cold and diminishes a bit as engine warms. However smoke, more black than white, never goes completely away now.  Previously, I never noted any smoke after warm up. 


I’m familiar with detroits, not so much with cummins, I’ve never had a pair of cummins. I have several friends who have them in their boats and they like the brand and say they’re well built. But that is the extent of my cummins-specific knowledge, so take this for what it’s worth.

That said, what troubles me here is your description that the problem began with the same symptom appearing in both engines at the same time. And that they never did this before. In my mind this makes the odds of it being a mechanical problem pretty long. 

Again I have no cummins-specific knowledge, but lots of people here do and I expect one of them will chime in soon. I know Dick Moreland had your same engines. But when both your engines begin making black smoke at the same time, even after they’re warmed up and under load, then to me that would indicate:

1) Potential overload condition. Have you had the bottom cleaned lately? Have you recently switched to different props, or had your props worked on? Recently done anything to the boat that would add weight, or may have altered the alignment of the running gear? Does the running gear turn by hand with the gears in neutral?

2) Are you running the boat in colder water temperatures than usual? Most diesels will make some smoke when cold. With marine diesels the norm is they don’t warm up unless you put a load on them. My detroits won’t come up to operating temp unless you run them up, especially if the water temp is cold you can putt around near idle all day and they won’t warm up. If you’re just cocktail cruising and the water temp is cool, then some (but not excessive) smoke is to be expected under those conditions. At least with my engines, once you warm them up, they will stay warmed up and within the operating temp range, but you have to load them to get them there to begin with. Was the water temp colder than normal? Does your boat have block heaters, and did you use them in the past but not this time? Do you think you’re using them but perhaps the fuse is blown, or bilge water reached them? Did you recently have the heat exchangers cleaned ? Are the engine temps lower than normal on the gauges?

3) Fuel problem. Have you recently bought fuel from a different source? If you are running in cooler temperatures, are you having any gelling issues? 

4) Are you using any oil? Have you recently changed oil type or viscosity? When is the last time the turbo seals were done?

5) Potential carbon buildup. When is the last time you have run the boat on plane?

Also these are kind of out of order, in that #5 should probably be #1.

If like most of us with big boats and the price of fuel being what it is, you haven’t run the boat at speed in months or years and have spent a lot of time at lower speeds, you need to go put it up on plane for 20 minutes and see does your problem go away. You get carbon crust on the valves and oil in the intake that seeps past the seals after extended periods of low speed running that will cause this issue. Running them up gets rid of it. You don’t have to burn a lot of fuel to do it, my mechanic tells me to run the boat on plane for 15 or 20 minutes per every few hours of slow speed operation, and that’s enough to solve the problem. 

In your case if it’s been awhile it may take longer, run them at speed until the smoke clears.

When was the last time you changed air filters or inspected them? This where I would start my troubleshooting trail.

Also need to check very carefully for a small exhaust leak at the turbocharger to exhaust manifold connection as you mention both engines behaving the same.

It does not take much of an exhaust leak in the engine room to blind off the air filter from fine carbon particulates from the exhaust. This will give you black smoke at full throttle but usually a clean idle. This problem will usually cascade as the increasing smoke plugs the air filter even quicker.

A restrictive exhaust can also cause increased exhaust smoke. Be aware that an exhaust hose that appears fine on the outside can be delaminating in the inside and cause problems.

Bad injectors or injectors out of adjustment will give blue smoke at idle but will clear up almost entirely as rpm is increased. From what you describe, I would put injectors down in the middle of the possibility list.

Be sure to research and price rebuild of the injectors vs replacement. There are many qualified "Diesel Injection" shops that can rebuild, calibrate and test ( Spray pattern and pressure) injectors around the country.


Not a fuel issue ---- if your seeing black smoke now and it's on both engines she's either in an overloaded state or air is being restricted...

Is your recent black smoke issue accompanied by a loss of WOT rpms and speed?...indicative of being in an overloaded condition.

Have you done anything that could be restricting ventilation into the engine room?

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