Yanmar 4jh4 hte issues at low rev and oil vs rpm question

[etoimene]

Hi all!

I have noticed that quite often, when put in idle, engine dies (not immediately, but looses revs and eventually dies - 5-10 seconds).
It is more noticeable after longer run.

I use workaround to put it in neutral and give it a bit of a throttle to stabilize the revs.
Also, when starting I push a lever a bit over just clutch engage to add some throttle.

Father tried to increase idle mechanically (old school ) so now it idles at 900 rpm (too high) but issue is still there.

I have noticed that when refueling I have to be light on the "pistol" (got a splash back) so might be something with tank breather, but engine dies even after I open tank and then drive it for short time (15-20 minutes) at 1600 rpm (no way it can spend that much fuel to create a tank low pressure), but might be connected.

Some sensor?
Fuel pump?

Another thing I noticed this year is that engine can achieve 3200 rpm at WoT, and it was barely above 2950 before.
The only difference that I know of is different engine oil. I don't have the specification of that oil at the moment. Will take a look next time on the boat.
I find it hard to believe it can change that much.
Final boat speed is the same (6,5 m semi displacement hull - 17 kn).
Maybe rpm meter is gone? I doubt that.

Unfortunately, decent Yanmar mechanic is quite far away.

Any ideas appreciated.

[Tayana42]

I have a 4JHE so not exactly the same as your engine. Here are a couple of wild guesses or questions from me. Start with the obvious and easy things. Is your prop clean? There could be a partial blockage on the end of the fuel pickup tube that the fuel pump can’t overcome at low rpms. As the engine is losing revs is the exhaust making smoke and if so what does it look like?

[etoimene]

Clean hull and prop.
I'll have to see for the fuel pickup blockage. Never tried to disassemble that.
No smoke that I am aware of (always concentrated to keep the engine running), but I'll pay closer attention next time.

I guess it shouldn't be turbo issue at these low revs.

[Tayana42]

I don’t know anything about turbos but there are other people on CF who know more who I expect will chime in soon. The increase in max RPM after changing oil type is interesting. Best of luck.

[Compass790]

My suspicion would be air leak or fuel restriction without knowing your engine specifically as post 2 suggests. Try checking all the fuel lines & filters. Also blow back thru the line from tank.

Doubt very much that oil difference would account for increased rpm unless you changed from a mistaken fill of EP 140 down to 10w-30 or something drastic like that. But be sure you use turbo rated oil or its bye bye turbo. Most are turbo rated these days in 1st world but don't know where in the world you are

[etoimene]

Thanks for suggestions.
Found an interesting thread on similar subject.
Especially this last post.
https://forums.ybw.com/index.php?thr.../#post-6156542

"Unlike most engines, on the Yanmar the fuel lift pump and injection pump are combined."
"Replacement or reconditioning of the combined pump would be a very expensive exercise"

Hopefully, that is not the case.

[Compass790]

Yea I'd do what they did & fit a 12v fuel pump to avoid getting reamed by the Yanmar mafia. I did that just to do the seperate lift pump alone on our engine as locally the yammer mafia wanted about $250 US for it & wont sell you a diaphragm for our ysm8 single. I got a used one for $10 & a new 12v spare for the same.
I bet Yanmar was real pleased with the designer who made the combined lift pump/injection pump non user-serviceable. Mind you they probably rewarded him by increasing his work hours & the CEO awarded himself another 50 million.

[hpeer]

I have a 2007 4JH4-TE. I forget what the “H” adds beyond some additional horsepower.

I had some fuel contamination that messed with my pump. I had to send it iut to a shop for service and cleaning. The report back was that nothing was amiss other than it being dirty. My symptoms were different; mad 1,600RMP fws, rev or neutral. I suspect it was a dirty governor.

In northern latitudes I run a W30 oil and in tropics a W40 oil. I top out at 3,200RPM no matter which.

The other thing which could possibly be awry is the “anti smoke” device. If you have the same pump as I do take a close look and find coolant hoses going to the fuel pump housing. Then you will not a small push shaft that turns a shaft. This gizmo is a thermo that adjusts the timing advance for easy cold weather starting. When the engine heats up the thermostat moves the rod and adjusts the timing a bit.

Mine self destructed. It is fairly cheap to replace but you have to drain the coolant. It is not necessary to make the engine run, but does make enough difference that it may effect its operation a noticeable amount.

Just something different about this engine that is often overlooked. It may, or may not, have anything to do with your situation.

[Scubaseas]

Originally Posted by etoimene

Hi all!

I have noticed that quite often, when put in idle, engine dies (not immediately, but looses revs and eventually dies - 5-10 seconds).
It is more noticeable after longer run.

I use workaround to put it in neutral and give it a bit of a throttle to stabilize the revs.
Also, when starting I push a lever a bit over just clutch engage to add some throttle.

Father tried to increase idle mechanically (old school ) so now it idles at 900 rpm (too high) but issue is still there.

I have noticed that when refueling I have to be light on the "pistol" (got a splash back) so might be something with tank breather, but engine dies even after I open tank and then drive it for short time (15-20 minutes) at 1600 rpm (no way it can spend that much fuel to create a tank low pressure), but might be connected.

Some sensor?
Fuel pump?

Another thing I noticed this year is that engine can achieve 3200 rpm at WoT, and it was barely above 2950 before.
The only difference that I know of is different engine oil. I don't have the specification of that oil at the moment. Will take a look next time on the boat.
I find it hard to believe it can change that much.
Final boat speed is the same (6,5 m semi displacement hull - 17 kn).
Maybe rpm meter is gone? I doubt that.

Unfortunately, decent Yanmar mechanic is quite far away.

Any ideas appreciated.

Check valve clearances. Likely a fuel supply issue though. To rule out blockages in existing run a supply and return lines to a well secured Jerry jug of clean fuel.

There are two lift pumps. One electric one mechanical. The mechanical ones are pretty bulletproof. If using an aftermarket electric pump get. A. 6. To 8 psi one.

Oil viscosity orr brand will not effect idle speed.

[MartinR]

Originally Posted by etoimene

Thanks for suggestions.
Found an interesting thread on similar subject.
Especially this last post.
https://forums.ybw.com/index.php?thr.../#post-6156542

"Unlike most engines, on the Yanmar the fuel lift pump and injection pump are combined."
"Replacement or reconditioning of the combined pump would be a very expensive exercise"

Hopefully, that is not the case.

Not on my 4JH4E, which should be the same engine minus the turbo.

You probably have an air leak somewhere. Another alternative would be the governor. That would also explain the changed revs.