Cummins 6bt black smoke debug process

[Ron Odenheimer]

I’ve got a 1998 6bt that recently started to show black smoke at high rpm (at the dock and under way). There has been no change to prop or any other boat change and there has been about 3 weeks between a 150 mile trip and the first sign of this problem.
The marine repairs guys in the area are booked out 5-8 weeks so I’d like to find out how to go about diagnosing the problem myself.
Thanks
Ron

Topic

[Ken Mahren]

black smoke

It is a 1994 Cummins 6BT 210……
1- it has run fine for years
2 On doc in neutral runs fine, brought it up to 2200 rpm, no issues.
Turbo spins freely, had filter off and observed spin at @1800 rpm
Under load (on the water) at @1500 rpm starts to black smoke
cannot go above 1800 rpm, just smokes more.
so at doc, with filter off and turbo spinning, runs o.k.
under load does not.
If it runs o.k. at doc at 2200 rpm does that rule out turbo and filter?
What else could be causing this issue.
I Have never run WOT…. seems to be tempting fate🙄

engine always starts right up
is very (reasonably) quiet while running even at 2000 rpm.
mainship 34 repowered with cummins in 1994. Purchased 5 years ago.

[Tony Athens]

Post the history of the vessel as to your use..

Did the engine ever reach rated RPM or more ( 2600) and did it ever not black smoke?

Lift the hatch and post a good picure what your complete engine.

[Ken Mahren]

similar issue

6bt210…… I have a similar issue… at the doc, in neutral I can rev up to 2200 and above with NO smoke and no issues. Under load I start to get black smoke at around 1500 rpm and loss of power…. so my question is ..

1- if I can rev up to 2200 in neutral with no issues, then does that ELIMINATE the turbo and air filter? What difference occurs UNDER LOAD that would effect the air mix if it does not happen at idle. If I can eliminate the filter and turbo, what next?

1 user thanked author for this post.

douglasharbison

[David Wesner]

I’ve had black smoke at higher RPMs. My engine is a 250 cummins 6BTA FWAC. Some success has come from fixing the poor sealing injectors. New copper washers and removal of the soot that had accumulated, which….prevented the injector from seating correctly.

D

[Ron Odenheimer]

Thank you, another set of tests to add.

Thanks for the help so far. I went back to to the boat yesterday and replaced the airsep filters and recovery hose but still with a lot of black smoke under way above 1800 rpm and wot was limited to 2000.
At the dock wot is about 2800 rpm so it appears the load makes the difference.
I’ll have to add the gauges if I figure out what parts numbers and where to find where to get them. Maybe at Seaboard?

[Clark Leighs]

+1 for gene fuller.

One possibility I will add is an exhaust restriction. If the exhaust air cannot get out then intake air cannot get in with the result there will be low power and dark smoke. A restriction will also show as low boost pressure and maybe a high EGT.

I believe that engine can stand a max of 3 PSI back pressure but check that figure to be sure. Other engines the value is even less.

You will need a low value pressure guage, 0 -15psi or 0 -10 psifor the needle movement to reasonably accurately show the back pressure.

In addition you will need to provide a port in the exhaust piping so the guage can be attached. Use about one or two feet of metal tubing first and then a good hose. The metal so the hose is not burned.
It need not be large, 1/4″ ID is plenty as the pressure to be shown will involve almost no air movement or flow.

The fitting will need to be mounted as close to the turbo exhaust outlet as possible so it will be HOT.

[Gene Fuller]

Unless there is rather catastrophic engine failure the black smoke and low RPMs means there is not enough air being supplied to the intake manifold.

Since that engine does not have an aftercooler the most likely causes are blocked air cleaner, loose or damaged air hose from the turbo, or the turbo itself.

All of these are pretty straightforward inspections. I would perform the inspections in that order. The first two would take only minutes. The turbo inspection can be done from the air side to check for a total lockup, but you will need to remove the exhaust elbow to take a good look at the exhaust side of the turbo. That is the most likely location to spot a turbo problem.

Gene

[Ron Odenheimer]

Black Smoke Reply

Thanks for all the reply’s. I’ve got some things to try or replace and will report back on results.
I’m still curious what a mechanic would do without trying each possible solution. Are there tools or gauges, in other words is there a way to make some test or get gauge info to help get to root cause?
We are headed to some remote parts of BC next spring/summer – it would be nice to install now when the boat is close to home, the appropriate gauges or get the appropriate tools to help narrow problems to fly the right part without need of multiple trips.
Happened to me a few years ago on upper Vancouver Is. with a Perkins 4-108 that would have needed parts from Campbell River via sea plane.
Thanks
Ron

[Terry Kerr]

Similar problems, came down to Aftercoolers

I had almost exactly the same problems on my 2001 6BTAs twice.

The first time was caused by a cracked exhaust on the port side, filling the engine room with soot and clogging the air filter. Fixed exhaust, replaced filter and was good to go.

3 years later, the starboard exhaust cracked (20 years old, so cant complain), followed same procedure as above, but this time not only were the air filters clogged, but both aftercoolers were full of soot and oil. Cleaned them as well and she is back on plane with zero black smoke.

Walker airseps are notorious for oil build up problems. Mine weren’t even installed correctly and had loops in the hoses that held a lot of oil. Tony called it a “War Zone”.

I tossed the Walkers and switched to Seaboard Envirovents. Only about an hour on the boat since the retrofit, but so far I think I am going to be happy.

[Ron Odenheimer]

More Info and something to check

I will check the turbo as soon as I get to the boat (maybe later this week).
It is a single engine 220 hp. The boat is relatively new to me but when purchased (almost a year ago now) the engine surveyor thought is was a solid engine. Has about 2000 hours on it. Just a few weeks ago it ran wide open at about 2900 rpm smoothly with no loss of power before throttling back. We ran most of our last trip of about 150mi at about 1500-1600 rpm. All was good. The boat’s been out maybe another hour after the last big trip, but did not check wide open throttle.
Now, when we push the throttle forward, the engine smokes above 1800 rpm and rpm will not go any higher even at full throttle.
So yes, both, smoke and loss of power.
At first I thought a rope or such had wrapped around the prop shaft , but it smokes at the dock, out of gear. It has a Walker airsep with the new filter sitting at my house waiting to be put in. There is a pinhole in the airsep housing that I need to plug , but I can’t see it affecting anything.
Any help is appreciated.
Ron

[Francis Valerio]

Do you have loss of power or RPMs along with the “new” smoking issue?

Is there any hard starting issues? cold? hot?

Fuel in your oil? (ck your oil level)

Give us as much info as you can about your engine and its history and hours?

Is your air filter dirty or restricted?

Is this a single or twin engines? (not that it matters really but more to compare the 2 if it is)

[Jeff williams]

I have a 6bt as well I would check the turbo hose to the intake for leaks if none pull the air cleaner and check that the turbo is spinning freely Black smoke is usually fuel not being completely burned I had the same problem with my 6bt intermittently and turned out the turbo was getting splashed with seawater on the exhaust side corroding it and stopping it from spinning due to improper exhaust Desighn
I’m sure some of the more knowledgeable folks will chime in but I think checking turbo is a good start

[Author]

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