Yanmar 3YM30 engine issues

[Patric86]

Hello everyone

I do have a little problem with my engine:
It is a 6 year old 3YM30, around 1400 hours. Maintained as described in the user manual. It starts to change / jump rpms. If it is in idle I hear every one to two seconds how the rpms roar up (the remote panel shows an increase of ~100rpms) for a very brief moment. At the same time the voltage on my batteries goes up, If I go to higher rpms the rhythm of the roar is quicker. There is no change if it is in gear or not. The Voltage goes up from 14.4 to 15 V, normally when my batteries are full and the engine is running the Voltage is at 14.0 or 14.1 V.
The rpm jumps are not in a perfect rhythm, if I listen carefully it sometimes takes only one second from one jump to the other and sometimes closer to two seconds but not regularly.
The last change I did was an oil change and I also replaced the fuel lines. It did run fine twice after that for 1-2 hours, so I don't think the change of the fuel lines could be the Problem? Although the sound makes me think that there could be air somewhere? But I don't get any success with bleeding the engine.
I did oil changes before, so I don't think I could have done something wrong there.
Could it be an electrical problem with the alternator that possibly changes the rpms?
Does any one here have an idea?

Thanks in advance
Patric

[Transpac 67]

It sounds like one cylinder is not running all the time. Maybe a partially plugged injector.

[Ziggy]

What caused you to replace the fuel lines?

[a64pilot]

Sounds like an electrical problem to me, volts going to 15 shouldn't happen, an alternator at full load will drop RPM by 100 or so depending of course on size of alt and engine


Sent from my iPad Pro using Cruisers Sailing Forum

[Ziggy]

My guess is you introduced an air leak when you replaced the fuel lines. Other possibilities (less likely) are plugged up fuel filter or bad injector(s).

[Patric86]

I changed the fuel lines because there were old ( 6 years ) and I had the feeling that I got air in there sometimes. But after the change the engine run twice for 1-2 hours without any problems.


I don't think it is a cylinder problem since the rhythm is not perfect.


I also suspect an electrical problem and I'll have an electrician here tomorrow.


Thank you for your answers so far, I'll let you know if I find something.

[Ziggy]

Do you have an Automatic Charging Relay (ACR)? I could see this behavior if it were cutting in and out.

[HappyMdRSailor]

Originally Posted by Ziggy

Do you have an Automatic Charging Relay (ACR)? I could see this behavior if it were cutting in and out.

+1

[GordMay]

Greetings and welcome aboard the CF, Patric.

[01kiwijohn]

Either disconnect the regulator, or the alternator, and see if it changes. Maybe, just take off the drive belt and run it for a short period. ( It shouldn't overheat if it is running without a load on the engine, for quite a while.)
Then you'll know, for certain, if it's fuel or electrical.

[mikequig]

I have a 3YM30 that had very similar revving problem with the engine - I changed the alternator because of a faulty voltage regulator - it shouldn't be putting out more than 14.3V - mine was putting out 15+ V and risked frying the batteries. By the way, I learned that the alternator was a Hitachi LR160-741 (60A output). You should be able to find one on Amazon/eBay for far less than what Yanmar wants for theirs. In my case, I needed a replacement immediately; couldn't find the exact replacement in time so wound up going to a local automotive repair shop and they found a Mitsubishi alternator that had the same dimensions and output and just needed a little soldering to add a tach output. Total cost: $90.

[ramblinrod]

Originally Posted by Patric86

Hello everyone

I do have a little problem with my engine:
It is a 6 year old 3YM30, around 1400 hours. Maintained as described in the user manual. It starts to change / jump rpms. If it is in idle I hear every one to two seconds how the rpms roar up (the remote panel shows an increase of ~100rpms) for a very brief moment. At the same time the voltage on my batteries goes up, If I go to higher rpms the rhythm of the roar is quicker. There is no change if it is in gear or not. The Voltage goes up from 14.4 to 15 V, normally when my batteries are full and the engine is running the Voltage is at 14.0 or 14.1 V.
The rpm jumps are not in a perfect rhythm, if I listen carefully it sometimes takes only one second from one jump to the other and sometimes closer to two seconds but not regularly.
The last change I did was an oil change and I also replaced the fuel lines. It did run fine twice after that for 1-2 hours, so I don't think the change of the fuel lines could be the Problem? Although the sound makes me think that there could be air somewhere? But I don't get any success with bleeding the engine.
I did oil changes before, so I don't think I could have done something wrong there.
Could it be an electrical problem with the alternator that possibly changes the rpms?
Does any one here have an idea?

Thanks in advance
Patric

An air leak in the fuel system can cause engine rpm changes, but the tell tale indicator here is the change in alternator output. 15 volts is (or should be) well above the regulator upper voltage limit (except in equalization mode if so equipped).
If you are familiar with electrical system safe working practices, here are some steps (in order of likelihood), try each one in turn, and check to see if that solved it before trying the next:

1. Verify the alternator output using a DVM (digital voltmeter), small panel meter accuracy can be +/- 2 volts. If it is truly 15.0 Vdc or higher, proceed.

2. Check your battery connections are clean and tight. (Remove terminals, clean, and re-install.)

3. Check your battery fluid level (and top up if necessary).

4. Check all connections between alternator and batteries.

5. Load test each of the batteries in isolation. (Replace if weak).

In many cases, this will solve the issue.

Never run your engine with the alternator "disconnected" from the batteries as this can damage the alternator.

6. If your charging system is equipped with battery ON/OFF switches, a 1/2/Both/OFF switch, or an ACR, ensure it is switched on to combine all batteries.

7. Check if your alternator regulator is equipped with an equalization mode, and if it is activated.

If problem persists, and the regulator is not in Equalization mode, it may be a regulator fault.

(While an ACR may switch in/out due to a bank voltage below the trip voltage, your alternator output should still not be going as high as 15.0 V if the regulator is working properly, in non-equalization mode.)

Ramblin Rod
Marine Service Provider
About Sheen Marine

[Patric86]

Here is a Little update what I did:

Day one: Started the engine, the rpms were clearly changing, I heard it, I saw it on the rpm gauge and I saw the voltage jump together with the noise.

Day two morning: I turned my solar charger off. I started the engine.
No Problem found.
Turned my solar Charge back on, started the engine again after a couple minutes, No Problem found!!!

Day two afternoon: Solar Charger ON, Engine started -> Problem occured.
Solar charger off after 5 min, Engine started -> Problem occured.
Tried again with charger off after 30 minutes -> Problem occured.

Day three morning: Solar Charger off, engine started wiithout Problems again.
¨
This makes me think the solar charger and the alternator are not friendly with each other. But how long has it to be off to not create a conflict? If I flick the Switch and then turn the engine on it works. But if the engine was on, then I flick the Switch of the solar charger that does not help. So I'm confused.

Or something with the batteries is wrong and if they are full, at the end of the day, the alternator doesn't like it. Could it be that the alternator is confused when he starts but the batteries are full? But this never occured when I use shore power to charge my batteries...


I hope this helps instead of bringing up more questions

Patric

[perdunulpart]

air in your fuel system seem to be out of question if your engine is always starting easily and check all your fuel line they will be greasy near your injector or fuel pump ,it sound like a voltage regulator working intermittency some time ok and other time bad,

[Ziggy]

Patric: you have a more complex system than I realized. Could you post a circuit diagram?