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Old 31-03-2020, 12:02   #1
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Yanmar 4 JH2E Diesel

I have a Classic Moody Motor cruiser which was fitted with a pair of Yanmars in the early 90ís.
These have always given excellent service and are still low hours. The boat is laid up undercover. Last week I decided to run up the engines using an external water supply. The port engine started after some churning but then increased in revs uncontrollably. The throttle cable was operating normally at the injection pump. The engine was last run 3 years ago when it behaved normally. The fuel is probably 10 years old. Any ideas why this happened? Iím reluctant to try again until the cause is established! Does diesel fuel Ďgo offí with age?
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Old 31-03-2020, 12:05   #2
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Re: Yanmar 4 JH2E Diesel

Would suggest this has nothing to do with fuel quality. More likely something like a gummed up governor in the injector pump or similar.
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Old 31-03-2020, 12:09   #3
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Re: Yanmar 4 JH2E Diesel

There are a few possible causes of runaway speed. The most common cause is the rings are not sealing and the engine is burning its crankcase oil. In that case the throttle has no effect.

How did you stop the engine?
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Old 31-03-2020, 12:21   #4
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Re: Yanmar 4 JH2E Diesel

Almost certainly a governor problem.
I’m order for one to run on oil it’s has to be hot, and I have never seen one do it by oil getting past the rings. I’ve seen fuel get into the oil until the oil level gets so high that the crankshaft beats it into a foam, then the foam goes out through the breather tube, which is of course connected to the suck side of the engine, then they run away.
If the rings were stuck so bad that they let enough out by to run off of, then there isn’t enough compression to start most likely.
I guess it’s possible, but I’ve never heard of it or seen it.
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Old 31-03-2020, 19:45   #5
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Re: Yanmar 4 JH2E Diesel

Iím curious to know how you got the 4JH2E to stop during the runaway, did the manual engine shutdown device work or were you able to block the air intake ?
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Old 01-04-2020, 00:00   #6
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Re: Yanmar 4 JH2E Diesel

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Originally Posted by skipperpete View Post
Iím curious to know how you got the 4JH2E to stop during the runaway, did the manual engine shutdown device work or were you able to block the air intake ?
Important question as it could point to where the problem is.

Also, what rpm was reached before you managed to shut it down - the answer might help in finding the reason for the runaway.
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Old 03-04-2020, 10:15   #7
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Re: Yanmar 4 JH2E Diesel

Thank you for your comments. Once it was clear that the throttle control did nothing I tried the electric engine stop no effect. Thought about blocking air intake but not accessible. Fiddled with ignition switch and stop button and it stopped. Discovered that the engine stop solenoid doesn’t work with the ignition switch off and suspect that in my panic I initially switched off the ignition prior to pushing the engine stop hence no effect! Not sure what revs were reached the instrument board is on the port side and I was rather busy!! Have just received the manual so hoping to get a clearer idea of what may have occurred. Fingers crossed it hasn’t caused any lasting damage.
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Old 03-04-2020, 12:10   #8
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Re: Yanmar 4 JH2E Diesel

Then you just have a throttle/governor problem.

If it were me I would cycle the throttle from min to max about 10 times and restart it. Be ready on the kill switch if it runs away.

Unless the revs go way past redline the engine will be ok. An unloaded diesel running at wide open throttle sounds scary but it is in no real danger.
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Old 04-04-2020, 10:07   #9
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Re: Yanmar 4 JH2E Diesel

I have a theory. I couldn’t understand why it would stick at a large throttle opening when the previous run up 3 years ago was at modest revs. Then I wondered if when the shut of solenoid is operated and presumably the fuel supply is cut does the governor attempt to open the throttle in order to maintain revs? If so the fuel rack might well have then stuck in that position.
Any thoughts.
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Old 04-04-2020, 12:36   #10
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Re: Yanmar 4 JH2E Diesel

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Originally Posted by kilmaine View Post
I have a theory. I couldnít understand why it would stick at a large throttle opening when the previous run up 3 years ago was at modest revs. Then I wondered if when the shut of solenoid is operated and presumably the fuel supply is cut does the governor attempt to open the throttle in order to maintain revs? If so the fuel rack might well have then stuck in that position.
Any thoughts.
That would presume that the shut-off was operated while the engine was running at high RPM. Who would do that?
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Old 04-04-2020, 20:29   #11
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Re: Yanmar 4 JH2E Diesel

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Originally Posted by kilmaine View Post
I have a theory. I couldnít understand why it would stick at a large throttle opening when the previous run up 3 years ago was at modest revs. Then I wondered if when the shut of solenoid is operated and presumably the fuel supply is cut does the governor attempt to open the throttle in order to maintain revs? If so the fuel rack might well have then stuck in that position.
Any thoughts.


On your injector pump the high pressure fuel is delivered to the injectors by individual elements in the injector pump which are constant stroke and variable volume,controlled very precisely by the rotation of the plunger helix through about 180įby the fuel rack which is in turn controlled by the governor via a linkage and spring.
For the sake of discussion we can make 5į the low idle point and say 170į the governed maximum rpm full load setting.... the other 10į is the cold start overfuel position and is controlled only by the pull cable thatís hanging at the rear of the injector pump ( the knob is marked coldstart)
And hereís the point........if just one of those plungers gums up and seizes, it locks the rotation of the other 3 and the governor ( and often the stop control too) canít push the rack to a low or no fuel position and you have a 3 cylinder ungoverned runaway, occasionally with catastrophic damage to the engine.
If this is what caused your un commanded overspeed you were very lucky that the stop solenoid was able to rotate the stuck plunger and shut er down.
Before you try another start, remove the air filter from the intake and be ready with a book or a bit of plywood to block off the air supply.
Interestingly only some racks get stuck in the full fuel position, many that Iíve seen and worked on stick in the no fuel.... no start position.
Pete.
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Old 05-04-2020, 01:42   #12
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Re: Yanmar 4 JH2E Diesel

Most rotary injection pumps and the introduction of common rail systems practically eliminated the seized rack runaway but introduced a new type of ungoverned overspeed....... mostly on automotive engines........ turbocharger shaft oil leaking into the intake.
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Old 05-04-2020, 09:23   #13
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Re: Yanmar 4 JH2E Diesel

Skipperpete thanks for your erudite reply. Can you recommend a fuel additive that might unstick the rack & plungers? As mentioned earlier the fuel is at least 10 years old. The tanks are plastic so no rust issue but maybe condensation though I imagine this is less likely with plastic tanks. Would you suggest draining and refilling the tanks with fresh fuel prior to my next attempt at starting? I intend to clean/replace the fuel filters and maybe prime the high level large filter with fresh fuel in any case. Out of interest where are you based? Regards Kilmaine
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Old 05-04-2020, 20:11   #14
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Re: Yanmar 4 JH2E Diesel

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Originally Posted by kilmaine View Post
Skipperpete thanks for your erudite reply. Can you recommend a fuel additive that might unstick the rack & plungers? As mentioned earlier the fuel is at least 10 years old. The tanks are plastic so no rust issue but maybe condensation though I imagine this is less likely with plastic tanks. Would you suggest draining and refilling the tanks with fresh fuel prior to my next attempt at starting? I intend to clean/replace the fuel filters and maybe prime the high level large filter with fresh fuel in any case. Out of interest where are you based? Regards Kilmaine


Hi Kilmaine
I donít know of any way of unsticking plungers after the event other than stripping the pump and even then itís often better to just replace all the elements rather than waste time trying to unstick them. For long layups there are some pump room tech fluids that are totally dry and low wax. Maybe un gas a small can of WD40 and bleed that through the pump as a storage fluid then bleed it out for the eventual restart? Not many people would go to this extreme though.
I have a concern that the plastic fuel tanks might in some way contribute to the problem, my own boat had the same ďJammed rackĒ issue and needed a pump overhaul at 180 hrs due to some ancient fuel in the plastic tanks. I found a layer of some sort of wax inside the tank and spent a lot of time with metre long Qtips and methyl alcohol getting that layer off ( made easier by the transparent tank).
I,m currently in Malaysia on Langkawi island in lockdown and my boat is in the south of France but no hope of getting back to it for at least 6 months.
Have you attempted a restart yet, if you only had a slightly sticky pump plunger it might have cleared itself. I totally agree with going through the entire fuel system and using new fuel from the tank right through to the injectors.
Pete.
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Old 10-04-2020, 09:25   #15
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Re: Yanmar 4 JH2E Diesel

Hi Pete thank you for your further message. A bit of background: the boat in question was my first boat purchase around 20 years ago and I enjoyed it on the Thames. I then got the bug and bought a 1965 Feadship, which is currently in Italy whilst I am in Surrey so I can sympathise with you being separated from your boat also! The old Moody is stored inside at home having had little use since the acquisition of the Feadship. However being in lockdown like you it seemed a good excuse to give her a run having briefly run the engines about 3 years ago. I will try and sort her out bearing in mind your advice! I have once visited Langkawi and stayed at the Casa del Mar a small hotel on the sea front which was excellent. Is it still there? And the lighthouse restaurant? Out of interest where is your boatís French Base? Cheers Kilmaine
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