Help w/ Yanmar 3JH3 Power Drop-Off Mystery

[ScottRhodes13]

Have you tried cracking the nut on each injector fuel line to see if the problem is related to a single injector? I had a similar problem, and it turned out to be a loose delivery valve guard where the injector pipe connects to the pump.

[Buena Vida]

We had a problem with our Yanmar YQM30. It turned out that the spare fuel filters that were on the boat when we bought it were too fine. I can't remember if we went from 5 micron to 15 microns, but after going slightly coarser we have never had a problem. In our case, after running for several hours the engine would die.

[betwys1]

Remarkably civil thread. No snippy comments. No irrelevant comments. Not much discussion on the injector pump though.

[john manning]

I agree with Wotname.

Have seen exactly the same problem with 3YM30's and 3GM30's. Coking in the exhaust was the problem.

[rla]

A layer of barnacles on the prop will give you these conditions easily !

[pendragon]

I had something like this also, the engine would not run up to speed. I found it was a partial coking up blockage at the the point where the cooling water is injected.

[reiner]

Originally Posted by Britishsea

I need some forum help diagnosing a engine problem that's past my mechanical skills.

I have a Yanmar 3JH3E with about 2000 hours on it. Engine was built in 2002.

I noticed that the engine was not providing max RPM ( about 2900 was my prior max) and assumed I had a fuel issue.

I changed the primary and secondary filters. Minor improvement was noticed that quickly reverted to the same problem. So I changed them again. No improvement.

So I changed the mechanical lift pump on the engine. No improvement.

I checked all the fuel hose clamps. All OK.

I happened to have had the injectors serviced last winter. I removed and installed them myself but had them serviced by experts. So hopefully it's not the injectors. I was told the injectors had a clean nozzle spray pattern but they were popping off early by about 15% - which they adjusted.

My engine will only now do around 2300 rpm. I can put the throttle all the way forward and no change after 2300. There is no smoke from the engine at all. It runs smoothly, no knocking or stutter.

One weird item I should mention...., for the 1st 30 min of run time from cold, i can get up to 2800 RPM from the engine. After that, it drops down to max 2300 RPM. The only thing i can think of is that fuel is getting hot after 30min and it's impacting some other system?

Any thoughts? Bad governor? Bad high pressure fuel pump. Engine too hot? Engine starved of air?

Thanks in advance for any advice you may have.

Britishsea

I had the same problem with my 3 cylinder yanmar 2006 model with around 1000 hours run
After trying all sort of fixed I found the mixing elbow where the cooling water mixes with the exhaust had rusted through inside the elbow. Installed a new one and problem solved
Hope this helps
Cheers
Reiner

[Britishsea]

Originally Posted by ScottRhodes13

Have you tried cracking the nut on each injector fuel line to see if the problem is related to a single injector? I had a similar problem, and it turned out to be a loose delivery valve guard where the injector pipe connects to the pump.

Thxs for the suggestion. I have not tried to crack the injectors individually, but note that the engine is running smoothly and there is no smoke in the exhaust.

Also, this is a problem that only manifests once the engine is hot. RPM will run as before until about 30 mins of motoring has elapsed.

I have a small hot water tank on the boat and it seems to me that it would take about 30min for it to fully heat up.

I am waiting for a replacement coolent temp sensor to arrive, as I discovered mine is closing its electrical connection when its tip is placed in boiling water.

[Britishsea]

Originally Posted by Buena Vida

We had a problem with our Yanmar YQM30. It turned out that the spare fuel filters that were on the boat when we bought it were too fine. I can't remember if we went from 5 micron to 15 microns, but after going slightly coarser we have never had a problem. In our case, after running for several hours the engine would die.

I changed the primary and secondary filters (twice), but no luck. My micron count is as before (5 secondary and 2 primary) - so should presumably not be an issue.

I did have some heavy seas this Summer, so I though I may have disturbed sediment in the tank. But the 2nd filter change made no difference to the issue - so I ruled that out as the cuase.

[Britishsea]

Originally Posted by john manning

I agree with Wotname.

Have seen exactly the same problem with 3YM30's and 3GM30's. Coking in the exhaust was the problem.

I replace my mixing elbow last year with one of these stainless steel mixing elbows : https://hdimarine.net/product/gm2jhb...-mixing-elbow/

If it was a mixing elbow or exhaust issue, it should present as problem whether the engine is hot or cold...

[Britishsea]

What about the stop solenoid? It cuts the fuel to the engine (as i understand it) to shut down. Are these prone to act up and partially engage? Or do they either work, or not work?

[Compass790]

It might be a wording issue about which is the primary filter.
As I read it the 2 micron is closest to the tank, what i would call the primary. I guess thats not the way you mean it do you mean the 5 micron is the closest to the tank?

[jt11791]

Originally Posted by Britishsea

I changed the primary and secondary filters (twice), but no luck. My micron count is as before (5 secondary and 2 primary) - so should presumably not be an issue.

5 micron is really small for the first filter. Most use 30 micron, followed by 5 or 2.

[Britishsea]

Originally Posted by Compass790

It might be a wording issue about which is the primary filter.
As I read it the 2 micron is closest to the tank, what i would call the primary. I guess thats not the way you mean it you mean the 5 micron is the closest to the tank?

I alway thought the 'primary' was closest to the engine and 'secondary' was the largest filter right after the tank. Sorry if i got these confused.

The 2 micron filter on the engine is specified by Yanmar, so I cannot go bigger than that.

The 5 micron filter at the tank is a Racor R20, so quite a large filter element for my 40 HP engine. I could easily run a 10 micron filter here.

[Compass790]

Originally Posted by Britishsea

I alway thought the 'primary' was closest to the engine and 'secondary' was the largest filter right after the tank. Sorry if i got these confused.

The 2 micron filter on the engine is specified by Yanmar, so I cannot go bigger than that.

The 5 micron filter at the tank is a Racor R20, so quite a large filter element for my 40 HP engine. I could easily run a 10 micron filter here.

I was just concerned you had the filters in the right order but assumed you probably did as you dont sound like you would make that mistake.
Yes 2 micron necessary for common rail final filter. As long as your flow rate is ok I dont think you need to worry, you proved that with no change in symptoms after you changed filter. If it worked ok originally you need to look elsewhere.