Question for the Cummins guys

[sillverchevy]

Guys,
Looking to hear thoughts on a couple nagging issues i've had with My 31 since purchasing 12 years ago. Engines are Cummins 6BT 5.9, 210 hp, 1998 with less than 1000 hrs.Boat runs very nice, cruises 22knts at 2200rpm, and can make full recommended rpms at WOT (2600rpm and 28knts)..HOWEVER, a few things I notice and would like to figure out. Port Engine, since purchase, consistently blows grayer smoke than starboard (which is white..steam). Enough to note soot on transom and clean monthly. Next, and more importantly perhaps, is the quick blow of black smoke when jumping past 1800-1900 rpm. This black smoke dissipates in 2-3 seconds, but always present when throttling up from below 1800 rpms. I'm thinking Turbo or injectors. The starboard engine blows a puff of dark grey smoke when throttling up for 2-3 seconds as well, but not black.Turbo appears clean, with no saltwater intrusion...spins free with little to no side to side play or up and down. Air filters clean as well. Also, on one instance this season, the port blew black smoke for 5-7 seconds when throttling past 1900, and the port engine would not rev past 2000rpms. this happened once, and not again, with both engines running normally, temp and oil pressures good. I took a video to show, but not sure how to post.
Thoughts guys?

[sillverchevy]

Here are the videos. The first is running at 2100 rpm.

https://youtu.be/QFovPHTAUAk

[sillverchevy]

This video is throttling up past 1800 (when turbos spool up) to 2400 rpm.
https://youtu.be/_3xkWdNIuH0

[Rawleigh]

Have you tried it with the aircleaners off?

[scenarioL113]

What is rated RPM?

If it is 2600rpm then can you make 2700RPM and make it easy? That is first question and that is what is recommended to make on B-series cummins (making 100rpm or more OVER the rated RPM)

Personally I think you have a bad injector that is "acting up"

See what others suggest on this thread and if you dont get a good direction to go in then I would pull the injectors and have them tested at a shop.

[sillverchevy]

Thanks for the replies guys.
Raleigh, i have not run the boat with air filters removed.
Frank, I cannot make 2700 rpm on either engine. now that I think about it, max rpm is 2650 on starboard, 2550 on port.

[Tony Meola]

The port tech might be off. Use a photo tach to check it. If it is correct then that engine seems to be loaded more than the starboard engine.

Have you had the props checked? Could be the port prop needs to be reset. Or there are issues with that engine.

If you need a photo tech, Harbor Freight has them. Mssy not be the best, but door your purposes it will work.

[scenarioL113]

Also

After you check all the basics and you believe all is OK (like the props, filters air and fuel, throttle cables adjusted properly, nothing caiught up in the props etc etc etc).
With that all checked and said then I would start looking a bit deeper. The one engine is def smoking and should not be.

Valve adjustment can be checked first before you pull the Injectors to verify they are set correctly.

If the injectors are tested at a shop and verified to be in proper spec than like I said earlier you will need to dig and test a bit further.

If the valves are adjusted properly and the injectors are good you could have a mechanic (or yourself) do a leak-down type test. You could have a valve that is not seating properly (burned valve or seat issue). I guess a compression test would give you an idea on that as well. I am just kind of throwing different things out there that can affect the proper running and cause some your symptom.

Keep us updated


To be honest after looking at your video I recall my engines looked similar to your port engine when I was overpropped and propping correctly resolved it.

BUT if this is a new problem then that may not be the direct cause but is more a contributing factor.

I think you ARE overpropped with an additional issue (like an injector or something)