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Old 26-01-2018, 05:33   #1
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Yanmar 3JH5E - difficult starting - advice please

Hi,

I have two Yanmar 3JH5E 39 hp motors on my cat. One of which is difficult to start, occasionally.

I prime each engine for 4 to 10 seconds before starting. One engine always starts, the other will either start normally or fire, run for a few seconds then stop. ( this may be a cold engine or a hot engine ie shut down for an hour or so).

To get it started I need to prime for about a minute. When it finally starts it runs normally up to max RPM of ~ 3000 rpm. Exhaust is normal, ie no smoke. Outside air temperature has been between 20 & 30 C. So not cold weather operations.

I have changed this engines fuel filter plus fuel/water separator. On draining water separator, there wasn’t any sign of water. These actions haven’t improved starting. Both engines have about 1900 hours. Fuel in tanks is less than one month old.

Where to next?

Advice greatly appreciated.

Thanks Brett
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Old 26-01-2018, 06:07   #2
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Re: Yanmar 3JH5E - difficult starting - advice please

If your engine runs fine once started, then the likelihood is that you have a fuel supply issue. Any air getting into the system in the fuel supply set-up will make an engine difficult to start. Pending the advice of those more knowledgeable than I, I would take a jerrycan of clean diesel and run a hose directly to the engine filter. Give the priming lever some pumps and then try to start it. If it starts O.K the problem is not with the engine. This way, you will narrow down whether the issue is with the fuel supply system or the engine itself.
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Old 26-01-2018, 16:06   #3
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Re: Yanmar 3JH5E - difficult starting - advice please

Could be several things, or combination of things, an air bubble trapped somewhere, a deteriorated hose, a blocked fuel return, a malfunctioning check or pump inlet valve. If you have a mechanical lift pump, that would be high on my list for suspected erratically faulty operation...

You might try bleeding the fuel system from several different, strategic points, starting at the first available point nearest the secondary filter, and working your way from there up the chain to the injector nuts.
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Old 26-01-2018, 17:22   #4
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Re: Yanmar 3JH5E - difficult starting - advice please

Symptoms seem to indicate that you have a very small leak in the fuel supply.

They can be the devil to find. Work sequentially and carefully and you’ll solve the problem. Shrink wrap or Saran Wrap can be a handy tool in eliminating possibilities.
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Old 26-01-2018, 20:06   #5
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Re: Yanmar 3JH5E - difficult starting - advice please

An engine with a fuel air leak, after running, the expansion of fuel in the lines exposed to heat will force fuel thru a leak or toward the tank, possibly past pump valves. When trying to start, the pump will draw air thru any loose connection because it's easier to move air than liquid thru a small hole.
The easiest way to find a small air leak in the fuel system is add a gauge somewhere and build fuel pressure above normal. Watch the gauge. If that doesn't show a leak install a fitting so you can put compressed air in the lines. Listen for the hiss. A bicycle bump is sufficient. Air escapes easier than fuel so often it's the air method that finds the leak.
Before all that trouble, check closely every connection from the tank to the injector pump. Maybe you'll get lucky.
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Old 27-01-2018, 11:04   #6
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Re: Yanmar 3JH5E - difficult starting - advice please

I would go with a small leak someplace in your fuel line. Just enough to suck some air.
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Old 27-01-2018, 11:23   #7
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Re: Yanmar 3JH5E - difficult starting - advice please

You shouldn't need to prime those Yanmars everytime. I had a small air leak that took me four years to find. It was so small that it only showed up if the engine had not been started for a week.

Things to check:

Replace both fuel filters using new gaskets and being especially careful to seat the gasket. Remember to wet the gasket with some fuel on your finger

Loosen each fuel hose clamp, pull the hose off the nipple and check for any cracking in the rubber of the hose. Use clamps with a "smooth" non-perforated band that won't cut the hose (AWAB makes some). If the hose looks old replace it. It's cheap.

There are plenty of other air leak culprits but the above will probably get 70% of them. I finally traced mine to the return hose that appeared to be 5/16" hose on a metric nipple. It was just a tiny bit big. When the clamp was tightened the hose would fold over ever so slightly leaving a tiny channel for air.
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Old 27-01-2018, 14:48   #8
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Re: Yanmar 3JH5E - difficult starting - advice please

That sounds like the fuel pump is not working properly,maybe a damaged valve in the diaphragm pump or you have a small air leak somewhere in the fuel line.

You are able to prime it manually--so the other alternative is the pump needs the tappet clearance checked. Maybe it simply is not pumping enough fuel to keep the engine running properly.


Sounds like a nuisance but it does not sound like the engine is damaged.
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Old 27-01-2018, 14:53   #9
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Re: Yanmar 3JH5E - difficult starting - advice please


Hi all .
I hope this isn`t the problem as it was a pain to fix as the fuel pipe ran thru bulkheads ect ,

My Volvo Penta D1-30 would suck the fuel line flat ,, it would stop the flow ,,
I would prime and Prime ,,

some times it would shut down , then i would have to wait till the fuel line popped open again ,,,
sounds the same to me ,,

Anyhow i changed the soft fuel lines to Hard pipe and never had the drama again ,,
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Old 27-01-2018, 15:46   #10
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Re: Yanmar 3JH5E - difficult starting - advice please

Quote:
Originally Posted by Robert Tilbury View Post
Hi all .
I hope this isn`t the problem as it was a pain to fix as the fuel pipe ran thru bulkheads ect ,

My Volvo Penta D1-30 would suck the fuel line flat ,, it would stop the flow ,,
I would prime and Prime ,,

some times it would shut down , then i would have to wait till the fuel line popped open again ,,,
sounds the same to me ,,

Anyhow i changed the soft fuel lines to Hard pipe and never had the drama again ,,
I would be investigating why there was so much resistance to flow/vaccuum to cause your fuel line to collapse personally. Dont know your engine but if it has a mechanical fuel pump that is going to be very hard on the diaphragm. Just a thought....
I'd agree with other posts saying OP's problem is small fuel leak. I found nylon washers worked better than copper on banjo bolts & they are much cheaper.
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Old 27-01-2018, 15:52   #11
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Re: Yanmar 3JH5E - difficult starting - advice please

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Originally Posted by Compass790 View Post
I would be investigating why there was so much resistance to flow/vaccuum to cause your fuel line to collapse personally. Dont know your engine but if it has a mechanical fuel pump that is going to be very hard on the diaphragm. Just a thought....
I'd agree with other posts saying OP's problem is small fuel leak. I found nylon washers worked better than copper on banjo bolts & they are much cheaper.
Thats the easy answer ,,,
Diesel resellers that put Kerosene in there diesel to strech out or water down there product ,, Kerro is taxed at 25% the rate of diesel ,,,,
Kero will make the inside lining of flexable fuel lines go like JELLY ,,

Not hard to see how the lift pump would suck shut the diesel lines when they are this bad
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Old 27-01-2018, 16:50   #12
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Re: Yanmar 3JH5E - difficult starting - advice please

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Originally Posted by Robert Tilbury View Post
Thats the easy answer ,,,
Diesel resellers that put Kerosene in there diesel to strech out or water down there product ,, Kerro is taxed at 25% the rate of diesel ,,,,
Kero will make the inside lining of flexable fuel lines go like JELLY ,,

Not hard to see how the lift pump would suck shut the diesel lines when they are this bad
Every picture tells a story! Thanks for educating me. Never heard of kero in diesel before. Wouldn't happen here as kero is more expensive. Surprised that kero would do that too as it's pretty similar to jet fuel isn't it?
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Old 27-01-2018, 17:03   #13
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Re: Yanmar 3JH5E - difficult starting - advice please

Hmm... interesting observation about kero and fuel lines - I have never had any issue with kero and flexible fuel lines but maybe it is dependant on the quality of the fuel line.

Off topic - I run my tractor on kero, jet A or diesel or a combination of any of those - whatever I have the most of at the time.

I do however only use diesel in the boat engine
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Old 27-01-2018, 17:15   #14
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Re: Yanmar 3JH5E - difficult starting - advice please

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Originally Posted by Wotname View Post
Hmm... interesting observation about kero and fuel lines - I have never had any issue with kero and flexible fuel lines but maybe it is dependant on the quality of the fuel line.

Off topic - I run my tractor on kero, jet A or diesel or a combination of any of those - whatever I have the most of at the time.

I do however only use diesel in the boat engine
I think certain types of fuel lines can handle kero ,, like some can handle Methanol ,,,

mine were soft very flexible ,,
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Old 27-01-2018, 18:19   #15
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Re: Yanmar 3JH5E - difficult starting - advice please

Chinese manufacturer of your fuel line???
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