Help w/ Yanmar 3JH3 Power Drop-Off Mystery

[Wotname]

Wait...is this a common rail engine?

And the issue only occurs when the engine has run for some time (i.e. hot).

If so, then it's a good chance heat related electronic issue in the computer controlled common rail injection pump.

I don't know very much about common rail injection pumps but I would try spraying copious quantities of freezer spray over the electronic aspects common rail pump next time the defect occurs.

If the power picks up right away, you have identified the faulty area.

[skipperpete]

That coolant sensor is meant to make contact in boiling water and ground the buzzer or light through the body of the sensor.
On, 97°- 103°

[kenbo]

Some confusion has crept into this thread. The 3JH3 is not a common rail diesel, it's indirect injection.

Britishsea check your manual, the on engine fuel filter from Yanmar is a nominal 10 micron. The recommended primary filter by Mack Boring, one of the largest Yanmar distributors in the USA, is 30 microns. I realized many believe that going with a finer filter is better but your diaphragm fuel pump doesn't agree.

Leaning towards a fuel delivery issue. Need to diagnose from the fuel pick up to the injectors one stage at a time.

[kenbo]

Originally Posted by skipperpete

That coolant sensor is meant to make contact in boiling water and ground the buzzer or light through the body of the sensor.
On, 97°- 103°

Exactly!

[wolfring]

Just a thought:


Max engine RPM, hull speed and prop should be matched for optimal performance. In other word, when you rev up to max RPM, and you hit hull speed in flat water your prop is properly sized.
My boat has a Yanmar as well and I went through this process when I picked my prop size. That was 11 years ago and it worked really well.
For whatever it's worth.


Wolfring
Tayana 48

[Compass790]

Originally Posted by kenbo

Some confusion has crept into this thread. The 3JH3 is not a common rail diesel, it's indirect injection.

Britishsea check your manual, the on engine fuel filter from Yanmar is a nominal 10 micron. The recommended primary filter by Mack Boring, one of the largest Yanmar distributors in the USA, is 30 microns. I realized many believe that going with a finer filter is better but your diaphragm fuel pump doesn't agree.

Leaning towards a fuel delivery issue. Need to diagnose from the fuel pick up to the injectors one stage at a time.

Thanks for the correction Kenbo. I assumed it was a common rail when OP said Yanmar specified 2 micron fuel filter which is not necessary on mechanical injection. I then lead Wotname astray. ( loved the freezing spray diagnostic tool tho Wottie ) Should have checked engine specs rather than following OP lead. I agree it likely fuel or air problem. We have no problems pumping with our 5 micron final filter but its 5x the size of the 10 micron original & our fuel consumption is tiny.
Apologies to Britishsea for my mistaken assumption.

[Wotname]

Originally Posted by kenbo

Some confusion has crept into this thread. The 3JH3 is not a common rail diesel, it's indirect injection.

.........

In keeping with the confusion theme, naughty Compass790 did lead me astray but I should have known better and checked myself.

FWIW, the OP has a 3JH3E which AFAIK, has direct injection but happy to be corrected.

[Britishsea]

Sorry to have dropped off this thread for a while. I had to wait 6 weeks to get a new thermo-switch from Yanmar's Georgia warehouse. Yanmar distributer has closed its local warehouse and stopped stocking parts...

New Thermo-Switch was tested (probe end in boiling water) and installed. It's set for 100C btw according to the stamp on the switch.


I installed a temporary clear hose on the RETURN line btw the high pressure fuel pump and the fuel filter body. I am seeing a small quantity of air in the return line. I am now assuming this is the culprit. So that's progress!

I tried to upload a video to show the amount of air in the return line - but even compressed to 1.5MB the forum would not allow the upload. it's a very thin stream of small air bubbles.


Thinking I may have a leak btw the fuel tank and the lift pump, I ran the engine off a jerry can with a hose directly to the lift pump. Still a thin line of bubbles air in the return from the high pressure fuel pump.

I tried to the bleed the system but no change.

One odd thing about the 3HJ3 is that according to the manual, its fuel system is 'self bleeding'. If it starts, it should bleed itself. Not sure however how long that process should take? Minutes, hours? I ran the engine for a good 20 mins at moderate RPMs.

Is there anywhere else that air might get into a marine deisel? I assume that everything after the lift pump is under positive pressure and so any faulty connection would not allow air to enter the engine? For example the fuel return lines off the injectors should not allow air to get into the system. Is that a correct assumption?

Any suggestions where to go next. I am about to give up at this point...

[Mike Banks]

Well, you have done all the things one usually does to stop air getting in.

The only other thing that comes to my mind is that this might be a little exhaust gas getting into the system via a faulty injector not closing completely, but having enough compression to fire the fuel.

[skipperpete]

Hi Britishsea, Putting the gravity feed line from the jerry can to the lift pump is not the best way to go, try going into the fuel filter inlet barb, as long as the jerry can is in the cockpit you should get you between 1 — 1.5 psi at 3 or 4 feet above the filter, (it will run perfectly on ½ psi) but be aware that the siphoning fuel will exit via the tank return line even when the engine is stopped unless you run the return to the jerry can as well.
Yes the fuel system is self bleeding and there should be virtually no fuel and zero gas discharge from the injector leakoff line to the filter. Verify by plugging the little flex hose with ,say, a small Phillips screwdriver on the filter side while you run the tests.
If all of the fuel supply system checks out as totally air free with a good flow, you need to consider either the injector pump as the culprit ........ or a simple mechanical problem like a head gasket blown between 2 cylinders rather than the more noticeable water jacket. Neither of these suggestions helps to explain the temperature to Rpm relationship though.

[Britishsea]

Originally Posted by skipperpete

Hi Britishsea, Putting the gravity feed line from the jerry can to the lift pump is not the best way to go, try going into the fuel filter inlet barb, as long as the jerry can is in the cockpit you should get you between 1 — 1.5 psi at 3 or 4 feet above the filter, (it will run perfectly on ½ psi) but be aware that the siphoning fuel will exit via the tank return line even when the engine is stopped unless you run the return to the jerry can as well.
Yes the fuel system is self bleeding and there should be virtually no fuel and zero gas discharge from the injector leakoff line to the filter. Verify by plugging the little flex hose with ,say, a small Phillips screwdriver on the filter side while you run the tests.
If all of the fuel supply system checks out as totally air free with a good flow, you need to consider either the injector pump as the culprit ........ or a simple mechanical problem like a head gasket blown between 2 cylinders rather than the more noticeable water jacket. Neither of these suggestions helps to explain the temperature to Rpm relationship though.

Thxs Skipperpete!

I will try the jerry can test again - by passing the lift pump as you recommend with the jerry can in the cockpit.

I will feed the return line into the jerry can as well. It's amazing how much fuel circulates back into the main tank at idle.

Just to clarify, I am currently running a clear hose between the high pressure fuel pump's return line and the filter housing (not from the filter's return line to the tank)- and that is where I am seeing the stream of air bubbles.

It makes sense that it could be the high pressure fuel pump. Could you expand on a cylinder - to - cylinder head gasket leak? How would that get air in the fuel system?

[skipperpete]

No, the head gasket was a different direction totally, you’re looking for power loss (rpm) and so far the discussion has been very much fuel related so sometimes it’s wise to re think everything. There are a lot of other possibilities including the auto advance, the pump Governor or its settings, even a high front pulley load from an overloaded alternator or belt driven accessory.
It’s the temperature/power(rpm) thing that’s got me stumped. Could it be somehow related to the driveline or gearbox I’m wondering. No black smoke at full load also challenges any theory that suggests overloading or blocked exhaust.
Pete.

[Britishsea]

Thxs Skipperete.

given there is air in the return line from the high-pressure fuel pump - i really think that's the most likely culprit.

The engine does not behave like it's overloaded or starving for air. It feels like a fuel issue. But always good to go back to basics in case it's something obvious that has been missed.

I will do some more testing before thinking about pulling the fuel pump - if that's even possible on a DIY basis.

[betwys1]

Originally Posted by Britishsea

I was down on the boat yesterday checking to see if I could narrow this power loss issue to a particular cause. /snip/

... I put a temporary clear hose from the last fuel injector to the primary fuel filter to check for air bubbles. Two observations from this test that surprised me. First there was basically no excess fuel flow from the injectors' overflow return, regardless of RPM or load (at the dock) . Second, there were no bubbles when the engine was running, but bubbles appeared once the engine was stoped. Perhaps there was some negative pressure in the return line on engine shutdown and the connection was leaking air. /snip/
Thanks again for all your help everyone who has commented above.

BritSea

I suspect you are being way too logical, and disregarding the Yanmar hint about cracking each injector nut. Why would you? It's a high pressure pulse. I can see the thought bubble even at this distance.
Like water hammer, fluid pulses attract a big transient low pressure pulse, and though proof against over pressure, a line may suck!

As soon as you accept this truth, you will fix the problem. Good Luck!

[Britishsea]

Good point. I did however crack each injector nut and it did not get rid of the air in the system. I do worry about a transient negative pressure on the supply line to the high pressure pump....but it did replace all these fuel lines with new ones and new hose clamps.

I will check again when i run off the jerry can (per. Skipperpete's advice, above) and remove the return line from the injectors (blocking it and the fuel filter's input nozzel for this line ) to see if that makes any difference.

I was looking at the this below thread last night regarding removal of the high pressure fuel pump for a 4JH4. https://www.cruisersforum.com/forums...al-209330.html

It looks like the same set up as my 3JH3. Anyone know if they are the same basic design (and more importantly removal procedure?). I will post some picture tonight...

BritSea