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Old 24-05-2024, 16:47   #1
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Yanmar 3JH3E won't start

We just returned from a year away from our boat. Engine started up instantly. But today we splashed, and though the engine started instantly, and idled happily in neutral, it died as soon as we put it in gear. This happened a few times. Now it refuses to start at all.

To me it seemed like a fuel issue, but tanks are full, and fuel is being pumped up by the fuel pump, as I just bled that. I also undid one of the injectors. Couldn't see the spray, as it was too awkward, so I put a piece of paper towel under the nozzle and it got wet with fuel, so presumably that means fuel is getting to the injectors. Didn't actually do this with the other two nozzles.

But still the engine won't start.

So at this point I am stumped. Why is my engine not starting? Any suggestions would be welcome!

Thanks in advance,
Noel
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Old 24-05-2024, 17:49   #2
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Re: Yanmar 3JH3E won't start

Diesels need only 2 things. Air and fuel. If you have fuel, check the air intake
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Old 24-05-2024, 22:50   #3
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Re: Yanmar 3JH3E won't start

S/V Illusion is right but I’d add heat as a third component, usually heat of compression but any heat’ll do.
One of the unpleasant results of long layups can be loss of compression but since it started and idled comfortably BEFORE refusing to start, I suspect a fuel problem. There’s occasionally cause to worry about the injector pump having a plunger stuck at the top of its stroke, this causes the other two plungers to lose the ability to rotate and regulate the amount of fuel injected, the amount remains fixed anywhere between maximum fuel and zero and can’t be controlled by the governor so you should consider opening up all 3 injector unions, checking that they all give about the same blip while cranking but more importantly that they all stop spurting when the stop is pulled. Best to close the raw water intake while you’re dead cranking to avoid flooding the aqualock.
Did you do any layup procedures that might stop the engine from starting? Sealed exhaust outlet or air intake? Fuel valves closed,?
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Old 27-05-2024, 17:18   #4
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Re: Yanmar 3JH3E won't start

Thanks guys. I am beyond my expertise, so I have someone coming to look at it shorly. I think there must be some gunk in the injectors. We shall see.
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Old 27-05-2024, 18:38   #5
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Re: Yanmar 3JH3E won't start

After the boat sat for a year, did you replace fuel filters or do any other maintenance before starting it up? What is the idle RPM? Did you crank it with the shutoff enabled first to circulate oil? What's the colour of the primary filter fuel bowl? Did you check for water? Was it cranked several times in the water with the thru hull open?
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Old 30-05-2024, 16:31   #6
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Re: Yanmar 3JH3E won't start

NO, before I started it I did not do anything. After it died I changed the filters and so on. No water in the fuel. Fuel color is red (marked diesel). Through hull is open and pumping water. Idling at the mormal RPM (700?) before it died.
Got a mechanic coming tomorrow, so we will see what he finds. I am suspecting the injectors.
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Old 31-05-2024, 09:23   #7
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Re: Yanmar 3JH3E won't start

I had a boat that idled fine but started choking when I revved it up. Turned out it was a bad seal in the fuel water separator. It only leaked air into the fuel system when revving the motor increased the vaccuum in the system
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Old 03-06-2024, 04:59   #8
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Re: Yanmar 3JH3E won't start

SOLVED! Turned out to be a loose nut on the throttle inkage that meant the engine was trying to start up and run at only 300 rpm or so. Obviously too slow. Before that the linkage wasn't accelerating when putting into gear and so the engine died, of course.

So everything is working now. Phew.

Thanks for all your replies.
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