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Old 27-12-2019, 13:27   #1
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Yanmar RPM issue

G'Day forum
2 questions:
Does the Yanmar 4JH4 have a rev limiting device that doesn't allow full rpm until normal operating temp has been reached?
I am only reaching 2000rpm, and only seeing a max temp of 74 degrees.
Despite changing everything (except the fuel pump), I have not yet been able to track down the problem (if interested, see another forum thread on Yanmar not reving past 2000rpm for a complete description of the drama)
The technical manual advises that the maximum exhaust back pressure is 20kpa, does anyone know what this represents in a column of water equivalent?
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Old 27-12-2019, 14:41   #2
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Re: Yanmar RPM issue

https://www.convertunits.com/from/kPa/to/inch+of+water[/URL]

20kpa = 80.4 inches of H2O according to above link.

Does it limit to 2000 RPM while in neutral, no load? If so, then it could be governor related or maybe not enough travel of your throttle control. the manual should show spec on throttle lever travel. Be sure engine stop solenoid is clear. I'm assuming this has a purely mechanical control system and not electronic.
Are you sure the tach is correct? That model may use the alternator stator pulses so is that charging properly (Clean DC output with AC component less than 100mV)?

My 2GM20F doesn't go above 3100 RPM, no load, using a 'laser' tach, though rated for 3600. It seems I need to change the factory set limit a bit, but your issue is quite different.
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Old 27-12-2019, 15:11   #3
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Re: Yanmar RPM issue

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Originally Posted by Toccata View Post
G'Day forum
........
The technical manual advises that the maximum exhaust back pressure is 20kpa, does anyone know what this represents in a column of water equivalent?
20kpa = 2.9 psi = 6.7'
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Old 27-12-2019, 15:31   #4
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Re: Yanmar RPM issue

Thankyou Wotname.
Much appreciated, will test today
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Old 27-12-2019, 16:20   #5
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Re: Yanmar RPM issue

You didn’t answer if it only does it in gear or not, if it’s also in neutral, that takes out a whole lot of possibilities

To my knowledge it has no throttle limiting devices.
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Old 27-12-2019, 17:53   #6
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Re: Yanmar RPM issue

The whole discussion is on the other thread.
To give you a quick rundown/summary:
Yanmar 4JH4 TE
127 hours total time from new (2013). Was running to full revs according to PO.
New Flexofold prop.
Engine won't rev past 2000 both in gear AND in neutral, ie; no load condition.
Changes:
New complete exhaust system. New Turbo. New elbow, New Vetus waterlock/muffler
New Vetus exhaust hose, New outlet, continuous fall from top of loop to outlet. Just tested exhaust back pressure at 10kpa (half the Yanmar spec limit)
Removed the hot water service and put in a small bypass hose. (not relevant really, but possibly disabled the cold start/pump time retard system, if there is an airlock in the bypass hose)
New complete fuel system. Clean/spotless fuel tank, New Racor, New fuel lines (return line too), New secondary cartridge. Tested with a fuel tank connected direct to the pump inlet, no difference.
I havent checked the valve/tappet clearance
The fuel pump is looking like the next check (I think)
The fuel tank was dirty with algae/crud in the bottom, I guess its possible some crud has entered the fuel pump, although there has always been 2 filters between tank and pump. Low hours and little use, algae growth in the pump??
Engine sounds as sweet as, certainly running on all 4 up to 2000
Notably it wont go above 74 degrees
I ran it at full throttle under load for 2 hours recently, no excess smoke and no change at the end of the run to the max rpm (still 2000)

All thoughts gratefully received.
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Old 27-12-2019, 17:57   #7
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Re: Yanmar RPM issue

If it won’t exceed 2000 RPM in neutral it’s the Governor, I feel certain.

If it were fuel restriction, exhaust backpressure or just about anything else it would rev higher in neutral than in gear, but not revving in neutral pretty much means the Governor is trimming it back

If 74 degrees is referring to Centigrade, that’s 165F, which is nearly perfect I believe, that’s what’s my thermostat is in my 4JHE.
They are not supposed to run hotter.

Now if its Fahrenheit, then you have a cooling system issue, most likely thermostat missing I’d bet.
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Old 27-12-2019, 17:59   #8
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Re: Yanmar RPM issue

Fuel pump off and get it serviced/overhauled I guess.
Can "crud in the fuel" cause this?
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Old 27-12-2019, 18:04   #9
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Re: Yanmar RPM issue

Quote:
Originally Posted by Toccata View Post
Fuel pump off and get it serviced/overhauled I guess.
Can "crud in the fuel" cause this?
Hi, before I spent any more on it I would find the most recommended small diesel mechanic/engineer/repairer in the area that has experience with that engine and consult with them first. Would be money well spent.
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Old 27-12-2019, 18:20   #10
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Re: Yanmar RPM issue

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Originally Posted by Toccata View Post
Fuel pump off and get it serviced/overhauled I guess.
Can "crud in the fuel" cause this?

Extremely unlikely, or said another way, yes it could limit fuel under power, but the fact your limited to the same RPM in neutral pretty much rules out clogged filters, air in fuel, restricted fuel line, plugged exhaust elbow etc, etc.

It is time to pay for a Pro in my opinion.
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Old 27-12-2019, 20:30   #11
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Re: Yanmar RPM issue

I suspect you're both right, I was just trying to solve it myself, practising for remote location problems, that said, I guess I couldn't buy a new turbo from a remote location...."smile face"
I will post the solution when found "hopeful face"
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Old 27-12-2019, 21:50   #12
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Re: Yanmar RPM issue

plus one for governor.
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Old 28-12-2019, 02:45   #13
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Re: Yanmar RPM issue

You could try to disconnect and operate the lever manually to be sure you are providing enough travel for full range. Otherwise it sounds like something is astray with the centrifugal governor. If an engine sits idle for a few years things can get rusted up on the various levers and springs in there. I've taken an HM35 apart to repair a broken internal lever which gave an engine runaway condition.
The throttle cable operates a lever that is really a speed control or "RPM goal". Internally, it pulls on springs to increase the governor setting. A spring may have weakened or broken. I'm assuming that you have similar traditional governor system.
See if there might be an inspection port to eyeball things. The shop manuals give very good drawings. There should an external adjustment of the RPM limiter, typically a screw wire-sealed at factory, but if that is not sealed now then it might be worth a slight tweak for diagnostic purposes.
The governor must, in the end, operate the fuel injection control rack (and individual pinions) which is the actual throttling -- of fuel volume injected. Not sure if there is an easy way to verify that full rack actuation.
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Old 28-12-2019, 04:59   #14
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Re: Yanmar RPM issue

Greetings and welcome aboard the CF, Dalestr.
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Old 11-01-2020, 02:37   #15
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Re: Yanmar RPM issue

Next Chapter
A Yanmar tech reviewed my progress today:
Fuel pump the most likely problem, probably caused by water in the fuel.
No puff of smoke on advancing the throttle, no smoke at full (although restricted rpm) he suspects it is just lacking the fuel volume to allow/cause higher rpm. (and smoke)
One interesting comment was don't operate it at wot until the pump is serviced, the risk is running the engine too lean.
Fuel pump and injectors off, and in for testing/overhaul.
I will report back.
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