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Old 23-05-2022, 14:22   #1
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Yanmar 4JH45

Well hello there.

Just got on my uncle's Leopard 42 with 2x Yanmar 4JH45s. Seems we have a little trouble starting the portside diesel engine. The engine cranks no problem, but doesn't seem to catch. We can get the engine to start by manually priming it (the auto primer no longer functions), but the engine dies as soon as its in idle.

When we manually prime the engine and get it to start, I'll throw it in neutral and give some throttle to make sure the engine runs, which it does. As soon as I release the throttle, the engine dies. We've replaced all the filters today, but it still doesn't work.

Couple ideas being tossed around here.
We've heard maybe it's got to do with the diaphragm?
We're thinking there's air in the system.
(see below)

Does anyone have any ideas? Please

Phil

EDIT: Tried correcting the title of the post, but don't know how to.
Also, it's a brand new boat. ~110 miles on it.
We heard it's possible that when assembling the boat, there may have been some debris that accumulated in the diesel reservoir. After some rough(ish) seas, it's possible this stirred up the debris, which flowed through the lines and caused a partial blockage. This would be enough to cause the problem.
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Old 23-05-2022, 14:36   #2
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Re: Yanmar 4JH45

for a few dollars, equip your engine with an automotive electric pump,
no more feed troubles, easy bleeding, no more diesel going into the engine oil span
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Old 24-05-2022, 01:40   #3
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Re: Yanmar 4JH45

Greetings and welcome aboard the CF, Phil.
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Old 26-05-2022, 10:48   #4
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Re: Yanmar 4JH45

I'm not sure that this is a bleed problem. A compression leak could result in the engine running at higher RPM but not at idle. It takes a small but finite amount of time for air to leak by (say) worn rings, and you could be in the intermediate state between good compression and not running at all.

I think that a compression check is in order.
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Old 29-05-2022, 23:42   #5
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Re: Yanmar 4JH45

Had a start issue with a brand new 3JH40 (similar design as yours). Symptoms were that it felt it cranked forever until it fired. Once it fired it tended to run, except once when I got a bad fuel alarm when running the engine a bit harder (about 2700 rpm)

It turned out that it was an oh so small leak at one of pre-filter fuel connectors. The banjees were to short to connect 2 clamps and 1 clamp did not seal the fuel line completely. The engine sucked some air into its fuel system vua this small leak. I ended up exchanging the fuel hoses against a different brand with a smaller wall. Since then it fires up in the fist fractions of a second. Apparently one clamp was able to seal this fuel hose.
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Old 30-05-2022, 00:38   #6
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Re: Yanmar 4JH45

Quote:
Originally Posted by bil56 View Post
for a few dollars, equip your engine with an automotive electric pump,
no more feed troubles, easy bleeding, no more diesel going into the engine oil span

Most Yanmars have lift pump integrated into the injection pump.
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