Yanmar won't go beyond 2200 revs. Help!

[boatbod]

Undercutter:- unloaded (neutral) max rpm is dependent on governor setting and is usually 200-400rpm higher than the max rated fully loaded rpm. On a 3600rpm engine you'd expect to reach at least 4000 before the governor would limit you.

Propellers should be sized/pitched so that the engine can attain at least the max peak nameplate rpm with wide open throttle and a clean bottom. Yanmar allowed you to exceed the max rpm by any amount, but under no circumstances are engine's to be set up overpropped and unable to attain their max.

Running an overloaded diesel will usually result in black smoke, foot in the exhaust and overheating/high EGT. It's as bad for the engine as persistent running at light loads.

[Copacabana]

Originally Posted by Hobiehobie

Thanks all for your wide ranging and thoughtful suggestions.

1. Take out the boat today on new tank of apparently clean fuel, see how she does in neutral, under load
2. Dive on prop again and check for fouling, turn prop in neutral see if there is any resistance, check feathering of Max prop
3 Change fuel tanks see if there is any change to eliminate pick up pipe issues

I have already: changed primary and secondary filters, checked sump of all four tanks for crud (none), checked prop for fouling (none...although I need to make sure it turns freely in neutral).

Will report back.

You might also want to have a look at your air filter or even remove the filter element when you do these tests. If you can, looking at the exhaust elbow to see if it's clear is also a good idea.

[seabreez]

Originally Posted by Hobiehobie

I have a Yanmar 4JH3 DTE 2007 engine in my Hylas 54. Just made the trip from Ft lauderdale to Virgin Islands and on the way experienced some engine issues. The engine would not go above 2200 revs, and was slow to get there. And at cruising 2000 revs was using much more fuel than normal (1.62 kph rather than normal 1.1 mph). In neutral will easily go up to max 3800 revs. No exhaust smoke of any color, 1700 hrs. No noticeable unusual vibration, and at 2000 revs the engine sounds smooth and normal. The bottom is clean. No unusual vibration in turning shaft.

I know the prop pitch is 1 degree off of the recommended, but don’t think this could be the problem, and it has been that way for a while but this rev problem is new.

The only thing I can think of is something around the prop, but the diver was down scrubbing the bottom last week and would surely have noticed?!

I will dive on the prop once out of the marina, but what else could this be. What symptoms to look for? Fixes? Any ideas friendly knowledgable forum?

With the above description, the next thing I would check is the air filter... the air flow has to be unrestricted. When this started to happen, what else happened? Anything different?

[hpeer]

Hobie,

What did you find from your new trial run?

[illanrob]

I have a Yanmar 3GMF 20 HP, max forward rpm are 3600. But have not tested those max rpms for 4 months.
Recently noticed that the throttle has to be pushed further to maintain 2600rpms while motoring at 5kts, so the throttle is approaching the max where it should rmp at +3000.
I am thinking that the 2 micron external fuel filter or the engine fuel filter may be starting to clog after 50 hours of use since the fuel tank was polished (filtered over 10 times while looking for debri). No smoke from this engine, engine oil level never chanes.

A clogged fuel filter could/would result in low rpms?

[a64pilot]

Originally Posted by illanrob

A clogged fuel filter could/would result in low rpms?

Absolutely, it is usually the first sign your filter is clogging, however with me it has never taken long before the first sign shows up and she will no longer run, as in minutes.
In your case, what you have sure sounds an awful lot like a fouled prop, you sure the prop is clean? It doesn't take much growth.

If you do change filters, remember there are usually two filters

[01kiwijohn]

are you sure the throttle linkage hasn't come loose, or slipped in its clamp?

[Toccata]

An old thread, but I too have a low revving Yanmar 4JH4 TE.
I have done the following:
New fuel supply system, primary and secondary fuel filters, new valves and fuel lines (supply and return).
Fuel tank scrubbed clean.
No air intake filter, just gauze
New turbo (I was sure this was the problem, alas no)
New waterlock muffler
New exhaust hose
New Flexofold Prop
2200rpm max at full throttle BOTH in gear and neutral
At 3/4 throttle it reaches 2200 rpm, then adding more throttle, the exhaust turns blue, but no increase in rpm (again both in gear and neutral)
Cable travel correct on throttle control
Today I checked the tacho with an independent device, all correct!
Any thoughts about where to look next?
I will come back and let you know what I find.....when it finally reveals itself

[sailing_gal]

Going back to basics, a diesel engine needs 4 things to run properly:
1)Enough air going in and it appears that you have checked that.
2)Enough diesel fuel being atomized inside the cylinder to produce power required.
3) Air and fuel going into the cylinders at the right time. This air intake is governed by the cam shaft which is set at engine assembly and the fuel timing is also set by a cam at engine assembly. So, both of these are unlikely culprits.
4) Getting enough exhaust gasses out appears to be the only thing left, especially since the blue exhaust indicates a combustion problem, either exhaust fuel or timing. If a complete exhaust hose has been fitted then we eliminate the inside of the exhaust hose swelling up like a balloon inside only when the engine is running. This leaves us with 2 last possibilities.

You could have carbon build up in the exhaust ports and valves, this would result in a gradual decrease in RPM over months as the carbon builds up.

If the fuel rack were not opening fully this would not produce blue exhaust smoke. Or, if one of the 4 delivery valves on top of the injector pump was broken or stuck this would restrict your revs but is unlikely to produce smoke.

Conclusion from here is a carbon build-up or blocked exhaust. If it is a carbon build-up, you can get rid of it by running the engine at full accelerator with a clear exhaust hose until the heat build-up. After about 10 minutes it would normally start blowing the carbon clear and the revs would increase. During this time you will see smoke from the burnt carbon. The smoke will disappear as the carbon disappears. The more proper procedure would be to dismantle the cylinder head, but you could give the cheaper method a try first.

My first test would be to run the engine at 1000 RPM, then use a #17mm wrench to loosen the injector pipe nuts one turn to see if all cylinders are firing the same. Do this to each cylinder one by one (tighten each one up after you loosen it before going on to the next one) using a cloth over the top to prevent any diesel squirting out and into your eyes (and everywhere else). This would eliminate pump problems.

One last possibility: If the engine does not fire evenly on each cylinder it could mean that you have a broken valve spring. This is easily found by removing the tappet cover and using a small wrench, tapping the valve spring holders on top to listen for a dull sound that normally indicates a broken spring. The normal sound is like a "ting". A wrench on the front of the engine will need to be used to turn the engine a full 2 revolutions bit by bit to get the valve springs fully up at the time of tapping. Check that none of the tappets have become loose due to a bent push-rod or locking nut.

[Toccata]

Thankyou Sailing Gal
The engine is a 2013 build. It now has 127 hours
The original turbo was clagged with carbon, and stiff to turn, ah ha problem solved. New turbo installed, no difference.
Air supply side fine
Fuel supply; the change in smoke from 2/3 throttle to wot, (causing more blue smoke) might indicate more fuel being supplied than can be burnt?
Engine sounds as "sweet as a nut" super smooth, so I conclude is running on all four pots.
The valve carbon issue would seem more likely than a fuel pump problem (at this low hours) Maybe a long hard run???

[Wotname]

Originally Posted by Toccata

An old thread, but I too have a low revving Yanmar 4JH4 TE.
I have done the following:
New fuel supply system, primary and secondary fuel filters, new valves and fuel lines (supply and return).
Fuel tank scrubbed clean.
No air intake filter, just gauze
New turbo (I was sure this was the problem, alas no)
New waterlock muffler
New exhaust hose
New Flexofold Prop
2200rpm max at full throttle BOTH in gear and neutral
At 3/4 throttle it reaches 2200 rpm, then adding more throttle, the exhaust turns blue, but no increase in rpm (again both in gear and neutral)
Cable travel correct on throttle control
Today I checked the tacho with an independent device, all correct!
Any thoughts about where to look next?
I will come back and let you know what I find.....when it finally reveals itself

Originally Posted by Toccata

Thankyou Sailing Gal
The engine is a 2013 build. It now has 127 hours
The original turbo was clagged with carbon, and stiff to turn, ah ha problem solved. New turbo installed, no difference.
Air supply side fine
Fuel supply; the change in smoke from 2/3 throttle to wot, (causing more blue smoke) might indicate more fuel being supplied than can be burnt?
Engine sounds as "sweet as a nut" super smooth, so I conclude is running on all four pots.
The valve carbon issue would seem more likely than a fuel pump problem (at this low hours) Maybe a long hard run???

Please confirm it has only 127 hours since new (or after the new turbo etc).

It sounds like an interesting fault and given all the things you have tried it might be a governor problem which would be unusual but I can't think of many other causes at the moment.

It doesn't take very much fuel to rev an engine in neutral so it in't likely to be a fuel supply issue.

However perhaps whatever caused the valve carbon and turbo carbon lies at the heart of your problem? Was this ever discovered?

All very strange for essentially a new engine (i.e. 127 hours).

BTW, unburnt fuel would be producing black smoke. Blue smoke is more likely to be oil burning - maybe this was causing the carbon. But again, only 127 hours????

[Toccata]

Yep, 127 hours only (total time)
Governor fault unlikely I guess.
PO did say they used to motor sail at low rpm.
The valve carbon issue is only speculation at this time, I haven't had the head off (trying to avoid that if possible)
The new turbo was fitted after considering all that's been done to the fuel supply side, additionally when I removed the air intake to spin turbo by the blades, it was found to be resistant to free wheeling, i.e. stiff to turn.
Possibly corrosion in the main bearing (or bush? this was considered a possibility due to wet exhaust/water vapour), but the exhaust side was also quite clagged with carbon.
I considered rebuilding/cleaning it, however the advice was that turbos now are considered a disposable item. (This advice from a truck service place) So big swallow ($) and a new turbo was fitted.
My next move is a long hard run and "see what happens"
Will advise the forum after completed.

[Toccata]

Yep, 127 hours only (total time)
Governor fault unlikely I guess.
PO did say they used to motor sail at low rpm.
The valve carbon issue is only speculation at this time, I haven't had the head off (trying to avoid that if possible)
The new turbo was fitted after considering all that's been done to the fuel supply side, additionally when I removed the air intake to spin turbo by the blades, it was found to be resistant to free wheeling, i.e. stiff to turn.
Possibly corrosion in the main bearing (or bush? this was considered a possibility due to wet exhaust/water vapour), but the exhaust side was also quite clagged with carbon.
I considered rebuilding/cleaning it, however the advice was that turbos now are considered a disposable item. (This advice from a truck service place) So big swallow ($) and a new turbo was fitted.
My next move is a long hard run and "see what happens"
Will advise the forum after completed.

[sailing_gal]

Taking the 127 hours into consideration after rebuild, I would suspect an old piece of rag or protection gauze that might have been placed in the inlet during the rebuild and perhaps sucked inside just before the intake valve? This would create a vacuum while the piston is trying to intake air thus allowing oil to move upwards past the piston rings. This partial air/oil combusted would produce blue smoke. Late injection timing also causes blue smoke. Late injection timing (360 degrees out) would show perfect timing marks and produce blue smoke and no power. This would mean that the engine could be injecting at the top, as normal, but between the intake/ exhaust strokes instead of between the compression/ power strokes. The engine might be slightly more difficult to start, but not always. It will run smoothly with no power.

To test this:
Remove the tappet cover. Remove the #1 injector pipe from the injector, turn the engine clockwise from the front while observing the 2 front valve springs. As you are turning the engine, a small amount of diesel should inject from the #1 injector pipe. At that point, the next quarter turn of the engine should move down a spring for the exhaust valve on cylinder 4 (one of the back 2 springs). If one of the front ones move downwards, the injection timing is 360 degrees out because the front springs should not move during that power stroke.

[Toccata]

127 hours from Brand New (Not rebuilt)
Gotta be something simple.......(please say yes)
I am hoping there is a gauze mesh in a banjo fitting and that this has become clogged with algae, or that my secondary fuel filter is clogged with algae. Todays job: bypass the secondary filter for a short test run, and check banjo fittings/unions