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I have a Yanmar 2QM15. I changed the secondary fuel filter…

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I have a Yanmar 2QM15...

I have a Yanmar 2QM15. I changed the secondary fuel filter the other day, and now my boat is belching out black smoke. When I originally changed the filter, I didn't realize the fuel had to be bled out. So I tried starting it 5 or 6 times over the course of 10 minutes. A friend came over and bled the fuel lines, which took a while. When the... Read full answer

I have a Yanmar 2QM15. I changed the secondary fuel filter the other day, and now my boat is belching out black smoke. When I originally changed the filter, I didn't realize the fuel had to be bled out. So I tried starting it 5 or 6 times over the course of 10 minutes. A friend came over and bled the fuel lines, which took a while. When the engine finally started again it began pushing out a lot of black water and smoke - leaving a carbon particulate on the surface of the water. We ran it for a while, and the problem continued. Eventually, the water and exhaust cleared up, but when I put the transmission in gear the RPMs drop dramatically and the engine puffs black smoke, as if it's under load. I had a mechanic look at it, and he suggested that the most likely cause is a clog in the exhaust mixing elbow from exhaust and rust (as it's a salt-water cooled engine). And since it's from 1980 it should probably be replaced.


 


Since it doesn't appear that there are any leaks in the lines we bled, I'm wondering if there are any other possibilities of what could be causing this issue.. other than a coincidence that the elbow gave out at the same time I replaced the filter.


 


I should note that when I started the motor in the past, a small amount of this particulate matter came out each time. Also we took the exhaust host off of the elbow this evening, and it looked like the elbow was about 1/4 to 1/3 clogged.

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Answered in 7 minutes by:
8/20/2013
Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11,504
Experience: 40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Hi my name is XXXXX XXXXX I will assist you.

 

Have you changed the primary fuel filter?

The things that will cause black smoke are. Clogged air intake, restricted exhaust, defectives injectors are the most common causes. From there is gets more serious. Leaking valves intake or exhaust, poor ventilation in the engine room restricting air flow and poor quality fuel.

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Customer reply replied 5 years ago

I have not changed the primary filter yet. That is on my list of things to do tomorrow. Could that have caused that dramatic of a change in the matter of a day, however? And could the exhaust output become clogged that rapidly?


 


A couple notes I left out before and couldn't add to the original question:


 


- Part of the time we ran the engine we were under sail. When the boat picked up a few knots, the RPMs increased - black smoke decreased - and the engine didn't sound stressed out. When the wind died down, however, the RPMs went down again.


 


- When I replaced the secondary fuel filter, I also replaced the air intake filter - which is working properly.

Ok do you know if you have any growth on the running gear or the bottom of the boat this can cause black smoke also?

 

If you have a fuel restriction the engine will not run correctly and cause loading and black smoke.

 

The possibility of this happening after the filter is most likely only coincidence.

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Customer reply replied 5 years ago

Sorry to sound ignorant, but what is the running gear? I don't think there is any growth at the bottom of the boat, but I can dive it in the morning and check through holes. My diver was last down there two weeks ago, but I've been sailing quite a bit.


 


Would you say my next steps would be to:


 


1) Replace primary fuel filter


2) Check for growth elsewhere on the boat


 


If I was to replace the primary fuel filter, how long would I need to run the engine to flush everything out (thus to determine if that was the cause)?

The running gear is the prop, rudder and shaft. If they become dirty or fouled with anything this will cause the engine to load and smoke.

 

If you bleed the system properly it shouldn't take more than a few minutes to get good fuel.

 

Do you notice any vibration out of the ordinary?

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Customer reply replied 5 years ago

Hi Tan,


I haven't noticed any vibrations out of the ordinary. When the engine running in gear and the RPMs dropped very low, there was obviously more overall vibration than when the engine is at a higher RPM.

Does the engine seem low on power? Have you changed the fuel filter yet?

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Customer reply replied 5 years ago

I'm going to change it this evening. Will let you know the outcome.


 


When I do a cold start on the engine with the throttle open, it takes a good 10 seconds for it to catch up to a normal RPM for that position of the throttle -- this is when the carbon particulate comes out. It struggles to get there, but once the RPMs pick up, the engine sounds normal until you put it in gear, after which the RPMs drop to a crawl.

You have either fuel injector issues or fuel supply issue. See what happens after the fuel filter is replaced. Now once the engine is running and it slows down open the fuel fitting at each injector does the rpms change. Be careful with this test as it will squirt fuel. This is a cyliunder drops test. The engine should loose the same amount of rpms on each cylinder. If there is a difference between cylinder noticeable then I would suspect that cylinder and injector. If one injector is acting up have al injectors reconditioned.
Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11,504
Experience: 40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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