Yanmar low RPM under load

[Wotname]

Originally Posted by ATC

Wow, the second time today, your exhaust mixing elbow is 'caking up' with carbon. This causes restriction in the exhaust and you have unburnt fuel, a reduction in RPM's and horsepower.

The OP has the semi straight mixing exhaust pipe and has already checked it; it is very easy to see if it had been blocked.

The OP has actuated the decompression lever on the #2 cylinder while the engine is running and there was no change in engine operation. Actuating the other decompression levers caused a change in engine operation.

Available evidence indicates #2 cylinder is not firing!

#2 cylinder not firing will result in loss of horsepower and lower rpm under load. The governor will increase fuel to no avail resulting in the OP's stated symptoms.

The OP needs to determine why #2 isn't firing. Checking valve lash is the next step (but there many other harder options at this stage).

Just my opinion of course .

[jmurray109]

The latest saga. The exhaust manifold was removed and each exhaust port had blockage. The first was about 33% and the the next 2 about 20-25%. Need to wait for gasket before reinstalling. Hopefully this was the cause, because the next step is above my pay grade. If you would like to see who I volunteer all this time to visit www.mariners936.com
We rely on a large amount of volunteers and donations to keep the cost down for the youth. Also the majority of our boats were donated and as you know when things are donated it was for a reason (old and difficult to get rid off). We spend a lot of hours to make them safe and usable for the youth.

[Wotname]

Originally Posted by jmurray109

The latest saga. The exhaust manifold was removed and each exhaust port had blockage. The first was about 33% and the the next 2 about 20-25%. Need to wait for gasket before reinstalling. Hopefully this was the cause, because the next step is above my pay grade. If you would like to see who I volunteer all this time to visit Mariners 936 |
We rely on a large amount of volunteers and donations to keep the cost down for the youth. Also the majority of our boats were donated and as you know when things are donated it was for a reason (old and difficult to get rid off). We spend a lot of hours to make them safe and usable for the youth.

Hope you are correct but if not, checking (and adjusting) the valve lash (tappet clearance) isn't rocket science and is something that you could learn in 5 minutes and teach to others in 10 or 20 minutes.

If you can remove / refit an exhaust manifold, you already have the hand skills and most of the tools. You will need a set of feeler gauges (should only be a few dollars). Google will tell you how to proceed but there are probably other people already in the organisation who know.

Looking forward to hearing what the final fix is.

[jmurray109]

Wotname, so I have been hesitate in doing the values, since I have never tried before. You are right it probably not rocket science, but I still want to watch a YouTube video first. I have the service manual so I have all the clearances and it even provides directions. In case you have not guested by now there has been no change. I have cleaned all the exhaust components, installed new injectors and accumulated a lot of grease under the finger nails. The one thing I was a little vague on was the cylinder compression check. At idle all cylinders have the same noise change. At 1500 RMP the #2 cylinder does not have a noise change, but you can hear a slight knocking sound. Also I spoke to the boat operator that was at the helm when this happened. He had been returning from Catalina (5 hours) and as he reached the harbor he idled down yo lower the sails and when he idled back up it would only go to 1800-1900 RPM. Once again thanks for all the help. I truly appreciate your advise.

[Wotname]

Originally Posted by jmurray109

Wotname, so I have been hesitate in doing the values, since I have never tried before. You are right it probably not rocket science, but I still want to watch a YouTube video first. I have the service manual so I have all the clearances and it even provides directions. In case you have not guested by now there has been no change. I have cleaned all the exhaust components, installed new injectors and accumulated a lot of grease under the finger nails. The one thing I was a little vague on was the cylinder compression check. At idle all cylinders have the same noise change. At 1500 RMP the #2 cylinder does not have a noise change, but you can hear a slight knocking sound. Also I spoke to the boat operator that was at the helm when this happened. He had been returning from Catalina (5 hours) and as he reached the harbor he idled down yo lower the sails and when he idled back up it would only go to 1800-1900 RPM. Once again thanks for all the help. I truly appreciate your advise.

The compression check is probably above your pay grade from the information you have posted although it isn't for difficult for those with the right equipment and experience. It basically requires the injector pulled and replaced with a compression check equipment but I'm thinking you won't have this stuff or experience.

Check the valves and if that nothing is found, you will have to call a mechanic or get serious about pulling the head etc.

Good luck and it sounds like you are doing a good job so far.

[jmurray109]

Originally Posted by Wotname

The compression check is probably above your pay grade from the information you have posted although it isn't for difficult for those with the right equipment and experience. It basically requires the injector pulled and replaced with a compression check equipment but I'm thinking you won't have this stuff or experience.

Check the valves and if that nothing is found, you will have to call a mechanic or get serious about pulling the head etc.

Good luck and it sounds like you are doing a good job so far.

So I forgot to mention that a chunk of the air filter was missing. It is unknown if this was new damage or has been like this for a while. That leads me to the next question. I have removed the air intake manifold and did not find anything. I have tried to dig out any debris from the intake and did not find anything that lead me to believe that I found all the missing pieces. I have tried compressed air to blow it out and also a vacuum. So it is still possible there is a large chunk down deep. What are my next options? This is the only thing that I have not ruled out as a possibility as a blockage. Someone also mentioned if not air intake that it could be something wrong with fuel governor. I am really tried to find something else wrong before saying that the #2 cylinder is dead. Any other suggestions would be appreciated. Thanks again.

[a64pilot]

The air filter deteriorating and the engine eating it is common, very common. It can’t be good for the motor of course, but I have never heard of it causing a problem.
Check the valves for goodness sake, it’s easy to do, then if not that remove the injectors and have them serviced. Being too tight if they are will damage a valve if you don’t fix it, if it’s so tight that it loses compression there is damage, hopefully not enough to not run right though.

If nothing else swap the injector from #2 to another cylinder, see if the problem follows the injector

[a64pilot]

You trouble shoot an engine by first starting with the easy inexpensive things first, sorting by highest probability.
Your doing hard, very improbable stuff first, just backwards of how to trouble shoot.
Pulling manifolds is as much work as pulling the head, and 100 times more work than checking valve clearance

[Wotname]

Yep, please listen to what A64pilot's says (posts 22 & 23) and save yourself a lot of heartache.

[Suijin]

Originally Posted by a64pilot

You trouble shoot an engine by first starting with the easy inexpensive things first, sorting by highest probability.
Your doing hard, very improbable stuff first, just backwards of how to trouble shoot.
Pulling manifolds is as much work as pulling the head, and 100 times more work than checking valve clearance

And if nothing else valve lash should be checked on a new-to-you engine and after adjustment it will run smoother.

It’s not hard. Do it.

[jmurray109]

Sorry guys that I have not responded to your suggestions. Yes I did the valves and there was no change. The valves were almost perfect, but hard to tell after loosening and tightening. I believe my final and last test will be a blow down into the cylinders. After this I give up. Thanks for all your suggestions. I should be awarded my basic Diesel engine repair certificate after this experience. If anyone is in the Dana Point California area and would like to assist, I will buy the beer.

[a64pilot]

OK swap injectors and see if dead cylinder follows the injector

[Wotname]

Open #1 & #3 decompression lever and try to turn engine over by hand, this will tell you if you have compression on #2. If no compression, pull head to check valve seats and to inspect bore.

If you have limited compression on #2, compare the degree of compression of #2 to that of #1 and/or #3.

[jmurray109]

The injectors were one of the first things that were inspected and replaced with new ones. I am leaning towards the head will probably be the next thing that is removed and the valves reseated.

[donradcliffe]

Having been through a similar exercise with a 3gm30f this summer, it turned out to be a blown head gasket on the #2 cylinder. No water in the oil or oil in the water, but the coolant was full of bubbles under enough pressure to lift the 15# coolant cap. I used the NAPA block test kit and confirmed that the bubbles were exhaust gases. The bubbles went away when I pulled the compression release lever on the #2 cyliinder, but not the other cylinders. After pulling the head and installing a new head gasket, all is well again.