Low power low rpm

[Frank Unsicker]

I have a 40ft vessel with twin Cummins 6bta engines.    My port engine low power/low rpm compared to Starboard.     Port takes a while to get up to 2600 rpm while putting out black smoke, white starboard gets up to 3100 rpm almost as fast as you push the throttle.  (The props were lowered from 22×22 down to 22×20 which allowed 3100+ rpm on both engines at the time.) Before I read Tony’s article on low power Idid the following:

1. Disassembled the racor 900 and cleaned the housing and installed new filter.

2. Replaced the Cummins fleet guard filter on the engine

3.  Pulled off all the fuel lines and blew thru each line

4.  Pulled the intake and returns off the tank and cleaned and blew back into the tank

5. Had the fuel polished cleaned<br />6. Replaced the fuel return valve on the P pump with a new one

7. tied the fuel shut off up with zip tie

None of this made any change in performance,   Then I read Tony’s article on low power and realized because I have black smoke it’s not a fuel supply problem.  After reading the article I tried the following:

1.  Cleaned air filter
2. pulled off Aftercooler and cleaned it throughly, cleaned heatX, cleaned trans cooler
3. checked all hose connections on the turbo for leaks and tightened up all hoses
4. adjusted valve lash
5. installed rebuilt turbo

After doing all the above I still have the exact issue.   I need some help about what to try next. Help    

Topic

[Frank Unsicker]

Issue resolved

After all the items I tried, it turns out to be a simple fuel supply issue.  The fuel hose from the Racor to the fuel transfer pump had a major kink.  I’m sure this was self inflicted.  When I removed the fuel coolers I rerouted the fuel lines to make access to the water pump ect.. easier and created a sharp bend in the fuel line.  Oh well live and learn!

[Francis Valerio]

Frank

Just keep working the problem, you will get to the bottom of it.  Just keep feeding us the data and we will do what we can to help you.

These are “mechanical” engines and are simple for the most part.  That does not mean that probs are solved easily but I assure you the problem is solvable.

Data is our friend BUT realistically it is not feasable to have a gauge or sensor to monitor every parameter that an engine could give you.  If you did tho, we would know the solution faster.   

Fuel PSI, Fuel vacuum, turbo boost, EGTs,  are just a few examples of parameters that can diagnose specific problems.

I second the idea of a possible propeller issue or a shaft.  It honestly does not take much to overload the engine when it comes to a running gear problem

[Tony Athens]

You have been thru all of this and yet you and missing tw0 basics.  

 

Tach accuracy–Confirmed at 2600-2800 at the dock, eng up to temp in neutral using a strobe on the front  dampener ( the color of the turbo and air pipe tells me you are way over propped and the rpms you are seeing are not what you think)  

 

 

measured boost at the  upper / top rpm from 2200-to WOT  on plane  ??    

[Frank Unsicker]

Injectors

Thanks for the suggestions!

 

The injectors are only a few months old.  Seems like if it was a compression issues it would be something that was changing slowly over time.  This happened over a one month period.   It may be a coincident but it happened after I changed all the fuel filters.  The SB article on low power low rpm says if its black smoke then its not a fuel starvation issue (I have dark smoke) plus I did try several new fuel filters, polished the fuel, blew all the hoses out, blew into the tank, new return valve.  The only thing on the fuel side I did not try was a new fuel pump.

 

[Francis Valerio]

How about the injectors?  Not sure if you checked them.  Maybe you have one just dumping too much fuel.

If the injectors are pulled then this is the obvious time to do a compression check.

 

Maybe a bad injector can dump too much fuel and cause “cylinder wash”. 

A stuck piston ring can cause problems like this but in my opinion that would be more that gray lightish color smoke but when underway if this was the case you can get loss of power and the other cylinders are now trying to pick up the low one and now you can see that black smoke possibly.

I dont think this is your problem, as I am only giving you ideas and oddballs that I have experiences over the years.  You never know.

You are covering all the bases but you need to know all cylinders are at PSI spec and same for the injectors.  Luckily this is not difficult on B-series.

After that you need to know the turbo boost PSI. 

[Frank Unsicker]

Turbo Hoses

I installed all three new Turbo hoses that I purchased from SeaBoard,  these hoses are a much better quality than the stock hoses. 

After installing the new hoses my RPM increased from 2600 to 2800 but it was still a much slower climb than the other engine which reaches 3050 almost immediately.

So the hoses made a difference, I do not know what to check next or what to try to get this engines to run as good as the other side.  Any more suggestions would be helpful.

[Frank Unsicker]

Valves

I pulled off all the rocker covers and checked and reset all valve clearance per spec.  .010 for intake and .020 for exhaust.  As I rotated the engine I watched all the rocker arms and springs for anything unusual but all looks good to me.

[Clark Leighs]

Have you had the propellors checked?    The port side at least.    They can get dinged without you being aware untill some work is done on them and the the difference is noticeable. 

  A ding or damage will add load to that engine.

A diver, a good one, can usually remove a prop with the boat being hauled.   If there is damage get it repaired and test again.

[Francis Valerio]

Did you check your valves and inspect the rockers and springs thoroughly?

[Frank Unsicker]

Rebuilt Turbo

I read the article on low power low rpm from SB and due to the Dark smoke I’m working my way down the list of Air issues.

“<u>LOW POWER / LOW RPM AND YOU HAVE DARK SMOKE:  </u>AIR issues: Not getting enough air can be caused by a dirty/collapsed air cleaner, a leaking turbo hose, a filthy aftercooler or air restriction inside the aftercooler, a worn out or partially stuck turbo, or a poorly ventilated engine room. Any combo of these can restrict air to the engine causing dark smoke and further, low power.”

I have tried all the items on this list.

Turns out there was nothing wrong with the old Turbo, I just wasted more money trying to resolve the issue and it made no improvement.  I’m still trying to figure out what to try next.

[donald roth]

In first post you said, “Installed new turbo”  —Why?   Turbos don’t just go bad for no reason!<br />The answer could be key to your problem.

 

[Frank Unsicker]

Hoses

I just ordered three of your HS-7502 hoses,  when they come in I will install the new hoses and test again.

[Frank Unsicker]

Explain it

Tony,  thanks for the reply

I did not take any pictures when everything was apart.  I did attach the few I took .

I can explain how i cleaned the aftercooler.

I un bolted the Aftercooler, put it on a vice, removed both end covers, slid the after cooler out. (It did not appear very dirty.) Then soaked the cooler in green degreaser for two hours, used a copper rod on each tube to make sure they were open, Sprayed the fins with 3 cans of carb cleaner, soaked it again for 30 minutes. Took my power washer and carefully washed all parts of it. Cleaned the housing with carb cleaner and soaked it also, then rinsed it with water.

Put it all back together using grease on each end. Installed it with new o rings.

It leaked water on the bottom side so I took the bottom cap off and noticed some corrosion so I used an over size thicker o ring and bolted the cap back on. This fixed the leak.

Ran the boat with no difference in performance.

 

[Francis Valerio]

Pull the valve covers and check your check your valves.  Inspect the rockers and makes sure they are OK.

I have had a bad rocker in the past that gave me a headache and also if any your valves are out of spec they can give you smoke and low power issues.

Make sure to take a good look at the valve springs as well, you could have a broken spring etc…  just a suggestion since you have covered all the other bases it seems.

good luck

 

FV

[Frank Unsicker]

Aftercooler

 

I un bolted the Aftercooler, put it on a vice, removed both end covers, slid the after cooler out.  (It did not appear very dirty.) Then soaked the cooler in green degreaser for two hours, used a copper rod on each tube to make sure they were open,   Sprayed the fins with 3 cans of carb cleaner,  soaked it again for 30 minutes.   Took my power washer and carefully washed all parts of it.   Cleaned the housing with carb cleaner and soaked it also,  then rinsed it with water.  

Put it all back together using grease on each end. Installed it with new o rings.    It leaked water on the bottom side so I took the bottom cap off and noticed some corrosion so I used an over size thicker o ring and bolted the cap back on.   This fixed the leak.   <br /><br />Ran the boat with no difference in performance.  

[Tony Athens]

Have I seen good pics on the installation, especially everything to do with the exhaust and turbo?   

Exactly what does this mean? Explain it.   

pulled off Aftercooler and cleaned it thoroughly   

[gskyward]

All ears…

After missing 2 summer cruising seasons in the NW due to re-rebuilds I’m all ears to any suggestions to mitigate any issues that would cause low power and slow acceleration.

[Frank Unsicker]

Low power

Thank you for suggestions, I’m ready to hear more.    It has no oil coming from the dip stick or anywhere else.   Would like to hear what the SB guys say.  

[gskyward]

Might Try This…

How many hours on the port engine? Have you noticed any oil leaking from around your oil dipstick? If so, you might want to check base pressure for excess bypass pressure. In addition, you might want to pull some injectors and boroscope the cylinders to check for scuffing or scoring, which could cause low power.

I just had both of my 6BTA’s rebuilt. 30 hours of running after the rebuilds I started to experience the same symptoms you described. It turned out to be excess pressure bypassing from the cylinders through the block due to improper piston-to-bore specs when engines were reassembled, which caused scuffing and scoring of the cylinders. In the process of rebuilding both engines again. Thank goodness for warranty work!

Hopefully, this isn’t your issue, but worth checking out to avoid any further potential internal damage.

Good luck!

[Author]

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