Yanmar 3ym30ae - loss of power

[Tactical Tony]

Hoping to get some advice from those far more knowledgeable than I on Diesel engines.
Briefly: My cat has 2 Yanmar 3YM30AE’s. Both under 1000hrs. Installed 2015.
Suddenly found port engine can only run to 2700rpm with black smoke billowing out. Other runs to 3100rpm.
Oil level fine. Checked props and no problems can be seen. Exhaust elbows never cleaned? (Someone mentioned maybe that’s a problem). Plenty of water flow out of exhaust though.
Anyone have any ideas before I get an expensive Yanmar mechanic in.
Surviving so far Phuket, Thailand.

[tkeithlu]

Quoting one guide:

Clogged Air Cleaner
Damaged Injectors
Bent Injector Nozzles
Incorrect Injector Timing
Clogged Air, Fuel or Oil Filters
Damaged Injection Pump
Damaged/Clogged EGR Cooler
Damaged Turbocharger
Damaged Intercooler
Over-Fueling the Engine
Wrong Blend of Diesel Fuel For Temperature
Cracked or Clogged Valves in Cylinder Head
Improper Valve Clearance
Low Compression due to Damaged Piston Rings
Excessive Engine Sludge Build Up

It largely comes down to too much fuel or not enough compression, because the black smoke is incompletely burned fuel. I suggest that you start by checking compression on each cylinder, and then check for wear on the injectors if the compression is OK.

[tkeithlu]

By the way, welcome to the forum, Tony.

[Copacabana]

Originally Posted by Tactical Tony

Hoping to get some advice from those far more knowledgeable than I on Diesel engines.
Briefly: My cat has 2 Yanmar 3YM30AE’s. Both under 1000hrs. Installed 2015.
Suddenly found port engine can only run to 2700rpm with black smoke billowing out. Other runs to 3100rpm.
Oil level fine. Checked props and no problems can be seen. Exhaust elbows never cleaned? (Someone mentioned maybe that’s a problem). Plenty of water flow out of exhaust though.
Anyone have any ideas before I get an expensive Yanmar mechanic in.
Surviving so far Phuket, Thailand.

Tony, if you are certain the fuel filters and diesel are clean, then check the air filter next. Better still, remove it and run the engine under load to see if the smoke goes away. If it's not a lack of air, then I would look at the mixing elbow as the likely culprit. I had the same problem with my Yanmar (losing RPM over time and increasing black smoke). I removed the manifold and elbow, cleaned the manifold and replaced the elbow with a new SS one and... voila! Back to normal RPMs and no smoke! I think this is likely your problem as well.

[Wotname]

First thing - inspect the exhaust elbow / water injection point for constriction.

[Scubaseas]

Originally Posted by Wotname

First thing - inspect the exhaust elbow / water injection point for constriction.

This. Exactly

[sengland]

Presuming you issue is when the boat is in neutral?
Start simple, for example....
have you checked ropes around the prop/shaft?
When was the oil last changed? Was it the right oil?
Does the engine throttle down at about the same speed as normal (Checking for drag or warn components), good that you have two engines so you can do a comparison.
Did the engine ever run hot? Alarm sounds etc...
When you run it, is there any additional vibration? (Indicating an issue with one of the three cylinders, which could be as simple as you decompress lever is actuated maybe just a little, or valves are cocked up or stuck open a bit)
Then maybe get into the injectors, fuel starvation through clogged filters, bad injector pump or blocked injectors.....

[Aqualibrium]

Too many people go looking for expensive fixes such as Injectors compression etc from my 50 plus years of experience Moët or exhaust restriction should be eliminated as possibilities first!!
These are easy checks and fixes that every boat owner should familiarise themselves with!

[Aqualibrium]

That should read
Inlet or exhaust restrictions
I’m referring to combustion air inlet here!!

[Aqualibrium]

Though a bottle of Moët might make you forget it temporarily!!
Gee I hate predictive text!!!!

[chasfgr]

Not enough air - air filters need a clean and new element (and no oil in them).
Try running them with filters off, if that clears the black smoke, problem solved.
Next is wrong grade of diesel (though my experience that even 30 degree heating oil runs OK in Yanmars)
After that it might be wrong injector timing by an incompetent mechanic, or someone has had the injectors apart and not rebuilt them properly.
Run through each likelihood, get the imjectors professionably serviced (they need it every 8000hrs ib any case.

[Wotname]

Just to reiterate - not enough air - most often due to exhaust system restriction which is often due to constrictions at the exhaust elbow where the water is injected.

Engine seems to run OK for years and one day it doesn't. The OP's symptoms are classic.

Anything is a distant second.

As many (but not all) have already posted

[Mike Banks]

I ran the same engine and if there is black smoke that means something is loading the engine and it is unable to reach the revolutions necessary for complete combustion of that amount of fuel. White smoke means no ignition.

I would suggest that the problem is as someone already stated--a blocked exhaust system. Carbon in the elbow is the most likely thing, the most easily checked and only a few hours to fix, less if one does not need to remove the exhaust elbow.

While at it, check that no one has left anything that can be sucked into the air inlet manifold.

[Wotname]

Originally Posted by Wotname

Just to reiterate - not enough air - most often due to exhaust system restriction which is often due to constrictions at the exhaust elbow where the water is injected..........

Opps... should have read 'at the exhaust elbow and mixing elbow where the water is injected'...

[skipperpete]

Originally Posted by Tactical Tony

Hoping to get some advice from those far more knowledgeable than I on Diesel engines.

Briefly: My cat has 2 Yanmar 3YM30AE’s. Both under 1000hrs. Installed 2015.

Suddenly found port engine can only run to 2700rpm with black smoke billowing out. Other runs to 3100rpm.

Oil level fine. Checked props and no problems can be seen. Exhaust elbows never cleaned? (Someone mentioned maybe that’s a problem). Plenty of water flow out of exhaust though.

Anyone have any ideas before I get an expensive Yanmar mechanic in.

Surviving so far Phuket, Thailand.

Do you have a high output alternator and smart regulator on this engine?... or any other additional crankshaft driven power draw equipment ( hydraulics, water maker pump)?
You only lost 400rpm at the high end so a rogue regulator might account for that loss of power and the black smoke.
If the problem occurred very suddenly, there is a vague possibility that the starter motor remained engaged, I see this with autostart gensets occasionally and it shows as a low frequency fault and shutdown. (Usually terminally damages the starter)
Pete.