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Old 11-07-2020, 11:35   #1
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Yanmar 3YM30AE diesel engine electrical issue

Hi All,


Looking for suggestions to help diagnose the problem. Engine is 5 years old, approx 500 hours on it. Two related symptoms:


1) Engine control panel powers up normally. But when I hit "glow" button, the panels turns off as if power to panel is completely cut. Panel will turn back on normally with the power button.



2) If instead of using the "glow" button, I just try to start the engine, the panel again immediately turns off in the same way. The engine does not turn over at all.


Checked batteries. They are fine. Connection wire from battery bank to back of starter/solonoid "looks" fine. Its a big job to start taking wires off really checking them, so I thought I would ask for advice first.


Generally speaking, I suspect this is probably due to a bad connection. But why would the control panel turn completely OFF? Do the symptoms provide any clues to which wires might be the problem?

From the service manual, it looks like the main power that feeds the engine and the control panel goes first to either the starter motor or the solonoid on the starter. From there, somehow, it appears to branch both to the yanmar control panel and the relay controlling the glow plugs... But it not really clear if this is one wire or two and where exactly they tie into the starter.

Any other suggested tests I can do to help diagnose? For example - to determine if the problem is the yanmar wiring harness as opposed to the main connection to the battery?


Thanks in advance!
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Old 11-07-2020, 11:42   #2
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Re: Yanmar 3YM30AE diesel engine electrical issue

Check out the very active and knowledgeable Yanmar Marine Engine Owners Group on FB
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Old 11-07-2020, 12:02   #3
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Re: Yanmar 3YM30AE diesel engine electrical issue

You say you "checked batteries" and they are fine. Not clear how they were checked, but batteries can show good voltage but have little or no capacity. A large load like glow plugs or a starter can draw the battery voltage down to near zero (turning the instrument panel off). So the batteries really should be load tested or checked with a hygrometer (if lead acid) to ensure that they really are fine.

If batteries are OK, there is likely a bad connection or component somewhere. I'd start by checking (removing and cleaning) the negative battery connection to the engine block. It's amazing how frequently this is the source of problems. Then check battery terminal connections and connection at the starter solenoid. Since this is triggered by both the solenoid and the glow plug relay it seems likely that the issue is upstream of the starter solenoid (somewhere between the batteries and the starter solenoid).
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Old 11-07-2020, 12:08   #4
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Re: Yanmar 3YM30AE diesel engine electrical issue

When you turn the key, something is pulling down the voltage available to the panel until it goes out. Ditto when you turn on the glow plugs. One bet would be that while the battery is sitting at 12.8v, it has no capacity and voltage drops like a rock when you turn the switch. You test that with a resistance load tester, $12.50 at Harbor Freight. Second possibility is a corroded or loose connection to the battery. It's fine, but because of the bad connection, only a low current can get through. That used to happen in cars - the lights would be bright, but the starter would not work, because the connection was loose/corroded. The third common cause in my experience is a shorted starter, but that doesn't explain it happening when you turn on the glow plugs.

Most of the time, you track down electrical faults by where 12.8v exists, with a voltmeter. In this case you can't do that, you need to track down where the amperage can't get through to turn your starter and light up your plugs. If you start at the battery, make sure that it is OK, and then clean and tighten each connection, you should find it.

Good luck with it.
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Old 12-07-2020, 06:53   #5
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Re: Yanmar 3YM30AE diesel engine electrical issue

Great suggestions. Will check out the FB group mentioned.

In lieu of load testing the battery, I set a volt meter on the battery terminal and watched the voltage (12.84 V) while I attempted to power the glow-plugs. It dropped to 12.82 V but no further. A proper load test would be better, I agree.


I didn't mention that I have two battery banks and have the same symptom with each one.

I will try monitoring the battery voltage from the starter and see if there any any drop there. The service manual says the glow-plugs draw 8-10 A, so for 3 of them the current draw is only ~30 amps. That seems a lot less than the 200+ amps the starter would draw.
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Old 12-07-2020, 07:31   #6
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Re: Yanmar 3YM30AE diesel engine electrical issue

You have a loose connection likely a ground, works fine until you attempt to draw current then because it’s loose / dirty it fails.
If it were the batteries, the voltage would tank, like drop to 6V or something, not a .2V drop.
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Old 12-07-2020, 08:42   #7
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Re: Yanmar 3YM30AE diesel engine electrical issue

X2 on bad ground/connection.
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Old 12-07-2020, 10:46   #8
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Re: Yanmar 3YM30AE diesel engine electrical issue

Had 3GM and now 3ym, 2 different catamarans. My, quite similar issue, engines 2005: battery to engine to panel (starter switch) back to starter solenoid, approx 20m. The voltage drop at the starter solenoid was significant, as for the size of our yacht I had to use the extension harnesses. Solving the problem was easy, I installed a cheap Hella 70A automotive Relais. The starter switch triggers the Relais, this Powers the starter solenoid. Never had a starter problem any more.
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Old 12-07-2020, 12:45   #9
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Re: Yanmar 3YM30AE diesel engine electrical issue

X3 it is a bad ground. Always check the ground first, easiest to do and 'almost' always the culprit.
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Old 12-07-2020, 13:15   #10
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Re: Yanmar 3YM30AE diesel engine electrical issue

Checking the voltage at the battery only tells you that the battery is OK. Watch the voltage at the panel. It will drop significantly when you switch on a heavy load.

I agree with the other posts - you have a loose or corroded connection or a bad wire.
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Old 12-07-2020, 14:18   #11
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Re: Yanmar 3YM30AE diesel engine electrical issue

If it were me, given your symptoms, I'd start at the batteries and work from highest amp draw towards lowest. Could be anywhere, but that's what I'd do. Not too likely at only 5 years old, but also check the primary cables themselves for anomalous stiffness, which would indicate internal corrosion.
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Old 12-07-2020, 15:26   #12
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Re: Yanmar 3YM30AE diesel engine electrical issue

Sounds like a bad earth or poor positive battery connection. The glow plug and starter relays are operating, but there is insufficient current getting to the engine.

Sounds like the earth connection--or negative connection--and it could either be in the engine room or on the starting battery terminal. Check ALL connections anyway.
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Old 12-07-2020, 16:46   #13
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Re: Yanmar 3YM30AE diesel engine electrical issue

Reading the thread again I cannot read that the solenoid even clicks or the engine makes the smallest movement. Maybe I overlooked that. If this is true it might be a stuck starter solenoid. That will pull tremendous current. A few hammer strokes while starting usually help. Btw, ever since I installed a starter switch in the engine room, just for convenience.
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Old 12-07-2020, 17:04   #14
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Re: Yanmar 3YM30AE diesel engine electrical issue

No, if you were pulling a huge load, the batteries would drop more than .2V.
A starter battery dropping to 10V is not at all uncommon during starting, of course a large house bank is not going to drop so much, but it would be more than .2V

On edit, I have seen a battery switch do this too, burnt or corroded contacts inside the switch won’t pass current, and act like a loose connection.
Not saying it’s that as that’s not real likely, but once you exhaust all other possibilities try jumping the switch
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Old 13-07-2020, 03:50   #15
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Re: Yanmar 3YM30AE diesel engine electrical issue

Quote:
Originally Posted by blubaju View Post
Btw, ever since I installed a starter switch in the engine room, just for convenience.
I have done the same, so much easier for any maintenance requiring engine rotation, i.e. bleeding the lines.
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