Low RPM & Black Smoke

[NoSpeed]

I have Cummins 6BTA5.9M3 330 HP@2800 RPM engines installed on our 2002 Bayliner 4788. The engines have logged approximately 1470 hours. I routinely operate the engines around 1500 RPM and cruise at about 8.5 knots. A couple of months ago, I was requested to pickup my speed to make a bridge opening and discovered the port engine would not accelerate to its rated RPM. In fact, the boat following me reported black smoke billowing out our exhaust during acceleration. Fire-walling the throttle was no help. Consequently, I had my mechanic investigate. At the dock, we took the port engine to 3140 RPM with no hesitation or black smoke. The air filters were cleaned at the end of last season. The primary/secondary fuel filters were also replaced at that time and vacuum gauges were installed. So, he said it could be the fuel injectors. Consequently, he replaced all 12 fuel injectors with new ones. On our next outing in mid-Sep, it was discovered this did not resolve the issue. The port engine could not sustain any more than 1790 RPM and the starboard engine would not accelerate past 2340 RPM. The discovery of the starboard engine having the same issue was not noticed earlier since I was using symmetric power. Now, my mechanic thinks it is likely to be caused by a torn diaphragm in the fuel injector pumps and suspects the use of Biobor JF as culpable. It has been difficult to get back on his schedule. Rumor has it he may have a serious health problem. Anyway, do any of you think this could be it? I am mechanically inclined to do routine maintenance myself. Would this be a job I could tackle or is it over my head? Where do I get the repair parts without buying completely new fuel injector pumps? Thanks.

Topic

[NoSpeed]

Rob, yes, these pics are of the core immediately after removal and prior to any cleaning. The two images are of both flat faces. The 2nd one is the air side facing the turbo. The housing is in excellent shape. There is no evidence of corrosion or pitting. I was able to figure out how to flip all the photos, so here they are again. I am now wondering if there is any good reason to do a sea trial just yet. After all, the turbos are just going to spit oil over my newly cleaned aftercoolers, right? Wouldn’t it be best to service the turbos now and then do a sea trial? Thanks.

[Rob Schepis]

So was one of those core pics prior to cleaning ?

How does the housing look at the sealing surfaces as to corrosion or pitting ?

[NoSpeed]

Well, it is finally the end of the boating season and I am beginning to address the issue directly. Attached are seven images of the aftercooler. I cleaned the port side first, as it was the worst. As you can see, there is nothing obviously wrong prior to disassembly. The two images of the core tell the tale. There was a significant blockage due by oil deposits from the turbo. The tubes were all clean as a whistle. The corner strips were not removed and no grease was used by the manufacturer. As Tony said, this is typical for a newly installed aftercooler. He was right! They were new as of 1000 hours. The boat has 1475 hours as of today. Removal of the core was extremely difficult since they did not use lube on anything. Cleaning was done per Tony’s protocol. Next weekend, I should be able to clean the starboard aftercooler. Then, I will conduct a sea trial. I am expecting better performance numbers, but am leaning toward the root cause being turbo related. I suspect the turbos are leaking an excessive amount of oil. If so, they should be sent to the shop to get new seals. I will report on the results of my sea trial, but does this logic sound right, seeing my port engine had signs of a minor oil leak in past years? Sorry, I was unable to flip these images.

[NoSpeed]

Rob & Tony, regarding my use of the word “flushing,” it is the term used in the Cummins Service Manual. I have read your article and watched the video regarding “Proper Aftercooler Maintenance. I will follow your advice. I have also read Tony’s “Understanding Low Power Troubleshooting” article. In it, you point to over propping or air issues as being culpable, not a dirty bottom. The likely suspects include a filthy aftercooler or air restriction inside the aftercooler. It seems prudent to perform a sea trial after cleaning them before investigating for a worn out or partially stuck turbo. Otherwise, if I found issues with both, I would never know which is at the root cause of my issue. I will not be doing your #1 as a first step since I encountered this issue with a clean bottom and running gear at the end of last season. Back then, the port engine only reached about 1675 RPM. Parasitic drag, alone, cannot explain the 550 RPM differential experienced now between the two engines. However, I do understand your logic in having a clean bottom in order to check the engines are operating at peak efficiency. Thanks for your help.

[Tony Athens]

Cummins recommends flushing the aftercoolers every 300 hours or annually. ,

This is ancient advise–Even Cummins saw the light about a year ago –100% ignore it and put the aftercoolers on the bench & get them apart–Take good pics of both ends just after you pull the caps!

What about 1,2 & 3 above?

You do want to solve this issue before something really bad happens, right?

Tony

[Rob Schepis]

“If there is water getting into the turbos, it is not obvious from the outside.”

It almost never is.

“Regarding a dubious exhaust system, it is a factory installation.”

Those are the worst kind.

“Cummins recommends flushing the aftercoolers every 300 hours or annually.”

Flushing? They need to be put on the bench and the cores removed from the housings so the air side of the cooler can be properly cleaned as well as the seawater passages.

[NoSpeed]

Steve, if there is water getting into the turbos, it is not obvious from the outside. Regarding a dubious exhaust system, it is a factory installation. Additionally, there have been no negative reports from my many mechanics or surveyors over the years. The boat spent its 1st lifetime in a salt water environment; the PNW. We became 2nd owners in Jun 2013. Since mid-2014, it has been mainly in fresh water; CA Delta. Tony, the port/starboard aftercoolers were replaced in Nov 2013. The engines had 1000 hours on them at that time. Cummins recommends flushing the aftercoolers every 300 hours or annually. They are overdue. I will get on it. The port turbocharger compressor housing was removed, cleaned, resealed and reinstalled in Dec 2013. Today, it has a very minor oil leak. I will try to get some pictures of these components, as installed, posted prior to the end of the boating season. Thanks for your advice.

[Tony Athens]

1) Pull the boat and have the the bottom and all on the running gear thoroughly cleaned–Props, shaft and rudders wet sanded w/ 80-100 G finish.

2) Take the boat out for a run–These engines need to “SEE” an easy 2900 RPM -2950 RPM–Not 2800–Write down what you see on the tach vs. dark smoke.

3) Post pics from all around–especially the exhaust, turbo and aftercooler

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Next — When was the last time the aftercoolers were removed from the engine and serviced on the bench per my protocol?

Report back AFTER you have accomplished 1,2,& 3 + the question on the aftercooler.

Until you do that, nothing else to do that will help you.

Tony

[Stephen Oliver]

If you are waiting then go easy on the throttles.. as black smoke generally goes hand in hand with high EGTs

Dont forget to post pictures as its normally obvious if the turbo is seeing water even from the outside.. and more obvious if the exhaust system is dubious.

Has it always been fresh water or only recently?

Steve

[NoSpeed]

Last bottom pressure wash and paint was in July 2017. We have been operating in fresh water since then. The issue I described in my OP, was the latest in a series. One of them was within 3 months after the bottom was painted. So, I doubt the condition of the bottom and running gear had a direct relationship to the problem. The props were not fouled because I had one of them sent to the prop shop for repair at that same time. That particular event triggered me to replace the primary/secondary fuel filters and add vacuum gauges at the end of last season. The filters were due for replacement, but it did not improve performance of the engines. I tend to agree with Steve’s assessment. I will inspect the turbos after our end-of-season use, later this month. Thanks for your feedback.

[Blair Ostergren]

Can’t reach rpm and black smoke usually means fouled props or dirty bottom. If you do a lot of slow cruising you may not notice it. I would make sure I have a clean bottom and test before getting into engine.

[Stephen Oliver]

First thoughts would be turbo’s

Need to see good pictures all around.. right back and close in – include exhaust and turbos…

until you post good pictures – dont do any more work. Black smoke – low revs and low power all point toward not enough air.. not fuel issues.. Chances are your turbos are rotten and not boosting.. caused by a bad exhaust design (I dont know the boat so dont know what is typical in them)

Have a look through my posts regarding my recent ‘adventure’ start here for some pictures.. https://www.sbmar.com/community/topic/bad-exhaust-result-on-turbo/ and then search through these https://www.sbmar.com/members/5teve/forums/topics/

If you are that way inclined – whip the exhaust elbows off (if they are standard cummins parts they are probably rotten and leaking internally) and have a look inside the turbos..

Steve

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