Yanmar stops in waves

[WolfgangSeaLife]

In rough bumpy seas motorsailing my Yanmar 4JH4-TE suddenly stopped. I started after a few seconds. It stopped again after a minute. I waited 2 minutes and started again, and it worked ever since. The waves could have been a little higher at the incident.
Temperature, oil, water, fuel all OK. Fuel and oil filters had been replaced two days earlier, not the 2 Racor filters (both were open).

What could be the reason? What to service? (I will replace the Racor filters).

Could it be a wacky sensor?

[Sailmonkey]

How much fuel was in the tank at the time? Large waves cause fuel to slush in the tank and the engine can pull enough air to shut down. Quite normal with tanks with flat bottoms and low fuel.

[WolfgangSeaLife]

Thanks, good point. Tank 1/2 full, 60 gallon, in flexible tank. Slushing quite a bit in rough gulf waves.
Wolfgang

[Zanshin]

Wolfgang - how did the engine stop? Suddenly, or with hiccups and surges, or just slowly down to 0? Also, does it start again easily or take a while?

Air in the fuel line takes a while to reach the engine, but also takes a while to bleed out (the Yanmar is self-bleeding, if I remember that one correctly), so you would need to turn on the ignition for a while, which gets the fuel pump to push out the air, before it will start.

[AA3JY]

Had similar experiences..plugged pick up tube from debris in fuel tank..ended up using positive pressure (mouth)through (disconnected) fuel line..yukkkk

Yes..in the end dumped a portion of the fuel though back washing the tank and fuel polishing procedure..

[WolfgangSeaLife]

Stopped suddenly, started after turning without hickups, but took holding starter longer than normal, about 10 seconds.
Same the next time.

[WolfgangSeaLife]

I have a fresh fuel filter, and I shone a light through both my Racor filters, they looked clear and clean, but I will change them.
Debris stirred up could be, air makes sense too.
The rocky waves continued for an hour, then two hours of smoother motor sailing. No further problems. But I hate this to happen in a rocky inlet.
Wolfgang

[PaulvR]

has been sitting for a while, his is a common problem. Gunk of various sorts accumulates and settles in quite water and is then taken into the pickup under suction, and clog....

Biocides help to avoid this, as does keeping the tank full when not in use, as well as sucking out the fuel tank 'sump' with a little hand pump before a passage if the boat has sat a long time.

[roverhi]

It's not the filters that you should be checking but the fuel pick up tube in the tank. Debris in the tank that is stirred up by boat's motion gets sucked in and lodged in the pickup tube shutting off flow. The suction in the pickup is stopped when the engine shuts down and lets the debris fall out so there is no obstruction when the engine is restarted. When you get in rough water again the sequence repeats. You should pull the pick up and check it out. If there is a fine mesh screen on the pick up, cleaning it may help. Removing the screen altogether sometimes works as well. On my old rovers pulled the bung on the bottom of the tank, drained the tank, then stuffed a garden house in the tank and let it flow for hours flushing most of the crud. Unfortunately that's not a possibility with a boat tank without pulling the tank. Maddening as you can't do much about it except pumping the fuel out of the tank, vacuuming the tank out and flushing it with fresh fuel or water.

[Zanshin]

If it were debris then the engine wouldn't want to start up and you wouldn't get RPMs. It does sound like it might be air which would cover the engine cut-out as well as the longer start-times. If it were debris then your Racors should be quite dirty

[Scubaseas]

With the engine running try wiggling the engine wiring harness especially from where the stop solenoid is at the injection pump. Also check the plug connectors. Ditto the ignition switch. If you fuel system is not the issue then your electrics likely are.

[PaulvR]

Originally Posted by Zanshin

If it were debris then the engine wouldn't want to start up and you wouldn't get RPMs. It does sound like it might be air which would cover the engine cut-out as well as the longer start-times. If it were debris then your Racors should be quite dirty

Not necessarily. In this case, after presumably a long harbour stay, the plugging occurs at the pickup in the tank itself. When the engine shuts down from fuel starvation, the plug is released (back into the tank), and so it restarts after a few tumbles relieve the fuel shortage, only to be plugged again ater as it sloshes around on a ocean passage..

[sailingchiro]

Sucked up a clog into the pick up tube. It clogged the fuel at the elbow out of tank. Once the vacuum stopped, the clog fell back down into tank. Will it happen again, most certainly. How do I know?
I had to take the dinghy pump to back blow the fuel line to unclog the line. Immediately came back to port and polished tank.

[dennismenace111]

When i bought my old boat I was told by the seller that the tank was full of fuel. Well, that tank was half full if water! We picked her up in Cape Coral and motor sailed to the Caloosahatchee where we motored across Florida to the ICW. All went well till we started hitting alot of boat wakes that stirred up the tank and drew water into the fuel system. Every 30 minutes or so we were cleaning the filter and bleeding the engine! Worked fine as long as the water was calm, but a 2 ft chop and we sucked water.

[ericoh88]

Not sure if a day tank could prevent the problem - yes no?