Yanmar dying

[carone]

Yanmar 4JHE 2000 hrs no prior issues with fuel side of engine.

Cruising at 2450 rpm, rpm's suddenly and mysteriously drop to 1100 rpm with some 'coughing'. After five seconds (seemed like 5 minutes) rpms slowly climb back to 2450 rpm. Dropping the throttle back to 1800 rpm, the engine operates smoothly x 20 minutes. Resuming 2450 rpm for five minutes and the rpm drop down occurs again. Rest of the day at 1800 rpm - No problems.

Background: Primary filter last changed a year ago (~110 hours of engine running since) , fuel purchased from busy U.S. marine fuel stop. No additives. No unusual rough seas experienced in prior days.

My plan is to change primary fuel filter and inspect. Any other suggestions/

Thanks

[toddster8]

Crud in the fuel tank. Upon inspection, also remove the pick-up tube and check the screen for snot and grit. Make sure all the hoses are clear of obstruction as well.

Make sure not to screw the pick-up tube in so far that it can ever butt against the bottom of the tank. I had to unscrew it half a turn.

Might also be a air leak, but only manifests when the pump is pulling against obstructed fuel flow.

My tank got stirred up during a rough bar crossing and led to a summer of issues. Eventually, I did a poor-man's emergency fuel polish using a Baja filter and a little hand pump from Autozone. And a pick-up tool for larger chunks. Got a lot of crud out.

[flpaoli]

Could you be lugging the engine because your prop is too overpowered? Is it pitch adjustable? If so, have you tried reducing the pitch a little?

[boatpoker]

Originally Posted by carone

Yanmar 4JHE 2000 hrs no prior issues with fuel side of engine.

Cruising at 2450 rpm, rpm's suddenly and mysteriously drop to 1100 rpm with some 'coughing'. After five seconds (seemed like 5 minutes) rpms slowly climb back to 2450 rpm. Dropping the throttle back to 1800 rpm, the engine operates smoothly x 20 minutes. Resuming 2450 rpm for five minutes and the rpm drop down occurs again. Rest of the day at 1800 rpm - No problems.

Background: Primary filter last changed a year ago (~110 hours of engine running since) , fuel purchased from busy U.S. marine fuel stop. No additives. No unusual rough seas experienced in prior days.

My plan is to change primary fuel filter and inspect. Any other suggestions/

Thanks

Change secondary filter too and buy a new lift pump. If that does not work you are probably looking at an injection pump rebuild.

[more]

Originally Posted by carone

Yanmar 4JHE 2000 hrs no prior issues with fuel side of engine.

Cruising at 2450 rpm, rpm's suddenly and mysteriously drop to 1100 rpm with some 'coughing'. After five seconds (seemed like 5 minutes) rpms slowly climb back to 2450 rpm. Dropping the throttle back to 1800 rpm, the engine operates smoothly x 20 minutes. Resuming 2450 rpm for five minutes and the rpm drop down occurs again. Rest of the day at 1800 rpm - No problems.

Background: Primary filter last changed a year ago (~110 hours of engine running since) , fuel purchased from busy U.S. marine fuel stop. No additives. No unusual rough seas experienced in prior days.

My plan is to change primary fuel filter and inspect. Any other suggestions/

Thanks

change all filter and fuel lift pump if still have problem

[Dockhead]

Originally Posted by boatpoker

Change secondary filter too and buy a new lift pump. If that does not work you are probably looking at an injection pump rebuild.

Those Yannies don't have a separate lift pump. It's built into the injection pump.


This is a typical boat diesel problem that in 99.9% of cases is caused by fuel blockage or air leak somewhere.


I have the similar 4JH3 HTE engine and in 4000 hours of use in my ownership have experienced the same thing a couple of times.



The Yanmar secondary fuel filter is extremely susceptible to clogging up, even when it's behind a 2 micron Racor (I know that doesn't make sense).


I stopped having these issues when I started religiously changing the expensive secondary filter even when I'm getting years between the 2 micron Racors, which I don't replace until they start to pull a little vacuum.



A tiny air leak will also do this -- I experienced that when installing Maretron fuel flow sensors.


Q to the OP -- what kind of primary filter do you have? Do you have a vacuum gauge? Have you had any fuel tank issues?

[carstenb]

We just had the same issues after about 6000 hours. hunted like mad. Take the fuel line out of the tank. There is probably a screen filter on the end of the tube that is clogged. If you have otherwise good filtration (we have a 5 micron Racor and then Yanmars own fine fuel filter), simply remove and do not replace the screen. The filters will catch anything that comes down the tube

[Tin Tin]

We had this happen too. Turned out to be tiny curl of aluminum caught in the elbow join to the primary fuel filter, believe it was left over from when tank was drilled for fittings. It took 4 years to work its way there. Happens in plastic tanks too. We were on a catamaran so were able to swap over fuel pumps and also compare discharge rates out of the fuel pump, one was a squirt the other a dribble.

[pcmm]

Originally Posted by Dockhead

Those Yannies don't have a separate lift pump. It's built into the injection pump.

This is incorrect. On a 4JH2E the lift pump is separate from the injection pump. Its mounted to the side of the injection pump and driven from it, but its physically a separate unit.

Look at your secondary fuel filter. The OP didn't mention anything about inspecting that one. Sounds to me like it needs changing. then check the pickup in the tank (if you have access to it) After that look for air leaks into the fuel system.

[Lou-In-NJ]

DON'T FORGET TO CHECK THE FUEL TANK VENT.
There are wasps that like to clog those holes with mud.

[Reeve21]

Had a similar problem on a 3gm30.

Tried many of the fixes mentioned above without success.

Problem turned out to be the secondary fuel filter housing. It was weeping and apparently letting some air into the system. Had probably been damaged during a filter change. If you can feel diesel on the bottom of the assembly it might be worth replacing it.

[pcmm]

Originally Posted by Reeve21

Had a similar problem on a 3gm30.

Tried many of the fixes mentioned above without success.

Problem turned out to be the secondary fuel filter housing. It was weeping and apparently letting some air into the system. Had probably been damaged during a filter change. If you can feel diesel on the bottom of the assembly it might be worth replacing it.

The 4JH's use a spin-on style primary fuel filter, completely different than the canister that the GM series used. Always made me nervous doing maintenance on the pimary filter as they were notorious for leaking and breaking threads.

Still possible that there is a clog or some junk in the sealing ring on the primary that is letting just bit of air into the system.

[Reeve21]

Originally Posted by pcmm

The 4JH's use a spin-on style primary fuel filter, completely different than the canister that the GM series used. Always made me nervous doing maintenance on the pimary filter as they were notorious for leaking and breaking threads.

Still possible that there is a clog or some junk in the sealing ring on the primary that is letting just bit of air into the system.

Good point about the different style of filter and one I should have realized since I now have a 4JH2E!

Am I confused about primary and secondary? I always call the Racor primary since it grabs the big stuff and the on-engine Yanmar filter the secondary.

[Dockhead]

Originally Posted by Reeve21

. . . Am I confused about primary and secondary? I always call the Racor primary since it grabs the big stuff and the on-engine Yanmar filter the secondary.

This terminology is confusing. You might want to call the native Yanmar fine filter on the engine the "primary" one, as in, the principle or main filter. That seems right to me and that's kind of how I would like to call it.

But you, and I believe most people, call the Racor the "primary", because the fuel goes there first. And the fine filter on the engine is the "secondary".

I force myself to use it like that so people understand what I mean. We should unite around one or the other terminology.

[CarlF]

As others suggest this is almost certainly fuel starvation. Incredibly common. Start with the simple solutions and do one thing at a time until the problem goes away.

1. Change both fuel filters.

2.Get fresh fuel

3. If the old filters look black you likely have diesel bug growing in the fuel. Clean the fuel and or tank. Start using a biocide like Biobar JF (this may temporarily cause more filter fouling - have spares)

4. Install a vacuum gauge. Every boat should have one as a way to monitor the fuel filter condition. If the gauge shows a high vacuum at high RPM check fuel pickup, tank vent, and consider replacing all fuel hoses if over 10 years old as old hoses sometimes delaminate internally

5. If you have a Racor, disassemble and clean the housing replacing seals and check valve (Racor sells a kit for this)

6 Only after ruling out all of the above look at the injection and fuel pump.