Yanmar 3JH3E Max 2500 rpm

[Frk. Jensen]

My 3JH3E engine from 2001 (1400+ hours) suddenly wont go above approximately 2500rpm under load. While not in gear there are no problems reaching higher rpms.
I normally run at about 2300rpm and do feel speed is as it has always been. Also throttle handle is at usual position. It's just like nothing happen when pushing it beyond the 2500rpm

Boat has just been on land, so everything is clean on bottom and propeller. All filters have been replaced either this year or last year

My guess is that it relates to fuel pipes somehow? What's the best approach to debug that?

I feel the engine sounds like allways, but think I read somewhere that it could be difficult to hear if one cylinder wasn't working. Any comments on that?

[Wotname]

Do the easy things first.

Check the exhaust mixing point / elbow for restriction. A restricted exhaust manifold / elbow will prevent engine from reaching full power. It can happen suddenly.

Checking / cleaning / replacing the exhaust elbow is a maintenance item. Yanmar recommends replacement every 500 hours.

[Tin Tin]

Might have a prop wrap fishing line or trace , crab pot line etc.

[skipperpete]

Originally Posted by Frk. Jensen

My 3JH3E engine from 2001 (1400+ hours) suddenly wont go above approximately 2500rpm under load. While not in gear there are no problems reaching higher rpms.
I normally run at about 2300rpm and do feel speed is as it has always been. Also throttle handle is at usual position. It's just like nothing happen when pushing it beyond the 2500rpm

Boat has just been on land, so everything is clean on bottom and propeller. All filters have been replaced either this year or last year

My guess is that it relates to fuel pipes somehow? What's the best approach to debug that?

I feel the engine sounds like allways, but think I read somewhere that it could be difficult to hear if one cylinder wasn't working. Any comments on that?

Since the boat has been “on land” has anything other than external cleaning been done to the propeller? Is it a feathering or folding propeller? Does the exhaust emit black smoke when “pushing it beyond the 2500” ? If one cylinder wasn’t working on a 3JH3, I think you’d notice it, maybe less so on a six cylinder diesel but definitely on a 3cyl engine

[Frk. Jensen]

Propeller and bottom cleaned. Same problem before and after.
I don't think exhaust has changed so I should probably disregard defect cylinder.

[Frk. Jensen]

Originally Posted by Wotname

Do the easy things first.

Check the exhaust mixing point / elbow for restriction. A restricted exhaust manifold / elbow will prevent engine from reaching full power. It can happen suddenly.

Checking / cleaning / replacing the exhaust elbow is a maintenance item. Yanmar recommends replacement every 500 hours.

I see many people referring the elbow, but wouldn't it also provide a problem while not in gear?

[Frk. Jensen]

Many people refers the elbow, but does it only affect the engine while in gear. While not in gear it easily goes beyond 3000.
Also i don't feel less cooling water is coming

Is it visually obvious if the elbow is worn? Can it be cleaned or should it be replaced?

Originally Posted by Wotname

Do the easy things first.

Check the exhaust mixing point / elbow for restriction. A restricted exhaust manifold / elbow will prevent engine from reaching full power. It can happen suddenly.

Checking / cleaning / replacing the exhaust elbow is a maintenance item. Yanmar recommends replacement every 500 hours.

[Wotname]

Originally Posted by Frk. Jensen

I see many people referring the elbow, but wouldn't it also provide a problem while not in gear?

It depends on how restricted it has become. The restriction increases the exhaust back pressure. The engine can cope with increasing back pressure but will deliver less power as the restriction increases.

Running to max rpm in neutral requires very little power so the engine can reach max rpm in neutral with a very restricted exhaust.

The water flow may be only slightly affected but the gas flow can be severely affected depending on the location and amount of corrosion present. You have to pull it off to see if there is any restriction internally.

[Tin Tin]

Depending on access the exhaust elbow should take about 30 minutes to remove unless nuts are seized. Google Images "clogged exhaust elbow" and you will see a multitude of clogged elbows. If this is the case you may save yourself thousands in engine repairs as the ramifications of a clogged elbow from both back pressure and potential water ingress can be quite severe.

[Frk. Jensen]

Well back from a long weekend I decided to have a look at my exhaust elbow.

It seems to be stainless and looks fine from the outside.
Having it dismounted (15min) I can see It is rather sooty, but in no way limiting neither water or exhaust from coming through.
I also tried filling it with water to see if it could leak from the outside to the inside of the inner tube. No water coming out in wrong places. I consider the exhaust elbow in fine condition.



Don't you agree?


Is the soot something I should be concerned about? I mean in general. Am I running the motor at too slow RPMs?

On most tours I'll use the motor in 15 minutes to get out of an harbor, and 15 minutes to get in. I.e. often it probably wont reach a good working temperature

[Wotname]

Yes, that exhaust elbow is in fine condition.

The soot isn't a big deal although it will only get worse. It would help if you ran the engine at load (WOT) occasionally. Yanmar recommends running at max RPM (in gear) for 10 minutes after every 2 hours of continuous low load operation.

Unfortunately it looks like it is back to the drawing board to determine why you can't reach max rpm.

[Frk. Jensen]

I had a pro visiting my neighbour boat shortly come in and listen. He said the motor wasn't running properly on all 3 cylinders. I probably need a fuel injection nozzle cleaning.

Yesterday I talked to my local Yanmar repair man who thought it was after all better to come by before concluding anything. He did agree on motor not running as it should and tried loosing up connection pipes one by one. Two of them made the motor die.The third made no change. It even didn't made any diesel come out. So at least this season it has been running at only 2 cylinders
His conclusion was a fuel pump issue. Easy and simple test. Don't know why I didn't think of that

Solving it probably isn't that simple. I'll get back when I have more information

[caipirinha]

Hi, my starboard-side 3JH has similar issues but occasionally : under moderate power demand (calm seas, little or no headwinds, progressive increase of boat speed) it will reach "normal" rpm (meaning my usual 1800-2500 range) but occasionally it will refuse to rev up (and usually that's when you need power quickly...)
Even when running "normally " it knocks more than the portside one so I suspect one cylinder does not deliver, whether for faulty injector, lack of compression, or ???
I'm really interested to follow up, likewise I will try to publish any findings on my side

[volition31]

You might try pumping out some fuel from the bottom of the tank and check for water. Check your racor water separator bowl for water. Have you changed both fuel filters and the air filter? Jim P.

[sinnerman]

If no fuel is coming out of the injection tube when it is disconnected from the injector, then you most likely have a stuck piston (plunger) in the fuel injection pump. This is usually caused by water in the fuel getting into the pump, sitting there, then corroding (rust) the metal piston.


You can try taping the injector pump with a screwdriver handle or plastic mallet with the engine running to see if it frees up.


Another option is to have an engine mechanic remove the delivery valve (threaded fitting where the injector tube attaches to the pump) from the top for that cylinder which is not working, and pour some penetrating oil into the plunger cylinder to break up the rust. See pic. Yellow is the plunger/piston...
(The other parts sitting on top of the piston are the delivery (check) valve which traps the fuel in the injector line aft er the injector fires...)


Cheers