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Old 12-29-2015, 09:43 PM   #1
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Yanmar wiring connector stopped engine from firing up

This morning after driving an hour from one marina to the next, my port engine would not start. It made no noise at all, just had the usual oil and battery lights on. Battery problem seemed unlikely as it had just been run and meters said batteries were strong. I verified that boat was not in gear or anything stupid like that. A boat mechanic friend happened to be nearby and he couldn't find anything wrong. Seemingly randomly, he disconnected a small white wiring block that connects to a small black wiring block (each holding about 4 wires) and damned if the thing hasn't started just fine all day. What the hell are those wires?

Engines are 4JH4 110hp Yanmars.

Thanks for the help!



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Old 12-29-2015, 11:45 PM   #2
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Connections corroded between the start key switch and the starter?

We had a similar situation this summer...with a trouble shooting guide in a Nigel Calder book we were up and happily running in about ten minutes.
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Old 12-30-2015, 12:03 AM   #3
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Aha! That sounds like exactly it. Thanks!
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Old 12-30-2015, 12:21 AM   #4
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Aha! That sounds like exactly it. Thanks!
You'd be well advised to confirm diagnosis with someone who has more experience than me
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Old 12-30-2015, 06:26 AM   #5
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Yanmar engines have a stop solenoid that engages when power is applied and pulls the stop lever. I suspect that power was being applied to that stop solenoid continuously when you tried to start due to some wiring defect. When your friend disconnected that cable connector it disconnected power to the stop solenoid so the engine would start.


With that connector unplugged you may not get alternator output or voltage to oil pressure or temp sensors.


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Old 12-30-2015, 09:52 AM   #6
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I also know on some Yanmar engines there is another relay in between the starter circuit that I didn't have in my book, also from my understanding they made an upgrade to that very relay from previous failures. Not sure if that is your issue just passing along some information. Good luck.
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Old 12-30-2015, 10:14 AM   #7
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...he disconnected a small white wiring block that connects to a small black wiring block (each holding about 4 wires) and damned if the thing hasn't started just fine all day.
(Note to self...be sure to re-read posts before offering advice.) In my head I thought your friend unplugged then reconnected the wires, which led me down the corrosion path.

djmarchand's answer got me to look at the Yanmar Service Manual for our 4JH2-UTE and found what he was talking about under, "Electric type Engine Stopping Device".

Apparently this happened to our engine in the past as well, because there were some notes I'd never noticed before from the previous owner of our boat on those pages.

Have you got the Yanmar Operation Manual, Service Manual, and Parts Catalog for your engines? Lots of info in there.
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Old 12-30-2015, 11:25 AM   #8
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Multi conductor plugs in engine systems can be trouble. On many boats I have cut the plugs out and butt spliced each wire. Or put a terminal strip in and landed the leads with crimp rings.
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Old 01-02-2016, 08:37 PM   #9
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Yanmar wiring connector stopped engine from firing up

For clarity, the connectors were reattached immediately after disconnecting and it's worked fine all week. Again, they were not left unplugged. The corrosion assumption still appears to be the correct one in this case. New connectors for both motors are being ordered. Thanks again to all for the thoughts.




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Old 01-03-2016, 12:24 AM   #10
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Use a good anti corrosion spray. WD40, Corrosion X, among others. It's simply to coat the pins and sockets in the plug with a moisture displacement coating.
This type of problem is NOT just a Yanmar thing. All the mfgrs. are using plug/sockets of some nature. It actually takes very little corrosion, more oxidation, to foul things up.
Unplug/replug will wipe enough oxidation off for things to work again. The spray stops a recurrence or at least for a longer period.

If the plug gets wet from leaks though all bets are off. If you have leaks then fix them.

Or do as SKI does.
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Old 01-03-2016, 12:52 AM   #11
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Use a good anti corrosion spray. WD40, Corrosion X, among others. It's simply to coat the pins and sockets in the plug with a moisture displacement coating.
Yup...and if it happened to one connection, there are others building corrosion as well. I've been systematically cleaning and spraying every connection from the helm station back, just in case.
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Old 01-03-2016, 06:56 AM   #12
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Great advice, fellas! Thanks.
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