Yanmar Cut-offs--Fuel? Something else?

[porschetrek]

I bought a 2012 Beneteau Oceanis 45 with a Yanmar 4JH5E at the end of 2020. Diesel ran flawlessly on delivery trip in 2020 and all of 2021. In July of 2022 diesel starting a pattern of cutting-out, but being able to re-start in a few seconds. Issue arises during steady RPMs, but probably moreso when adjusting RPMs up or down. Makes docking a little more exciting than needed. I've cleaned the Racor, and changed the secondary fuel filter, but haven't seen any changes. I plan on getting the fuel polished this week if feasible on this boat to see if that helps. Any other places I should look for causes?

[Jammer]

Did you change the element in the Racor?

[porschetrek]

Yes, replaced the element in the Racor, as well as the spin-on secondary filter

[chris mac]

Our yanmar used tiny fuel lines. I've had the elbow at the top of the fuel tank plug up. After polishing, it hasn't happened again. But it could be worth checking.

[Jammer]

1) confirm that the tank vent is working, apply gentle air pressure to the tank vent using the outlet of a shop vac or something, observe that air is coming out of the vent.


2) confirm fuel flow out of the tank, put a tray and pad under the racor, open the drain plug, operate priming pump on racor, observe that fuel flow is strong and there is no unexpected resistance. Problems here may indicate that the fuel outlet in the tank (and its screen if present) are plugged, or that something is plugging the line between the tank and the racor


3) operate electric fuel pump (turning the key to on) and check for flow in the fuel return line to the tank. Remove the return line from the primary fuel filter and observe that a good deal of fuel comes out the port (use a container and a pad to catch it, natch). Problems here may indicate a bad fuel pump.



4) put a scrap of hose on the fuel outlet from the primary fuel filter and put it into the bottom of a clear container. Operate the fuel pump. Let the container fill a little then see if you're getting bubbles. If the bubbles continue and don't stop you have an air leak somewhere.


If you get good flow in the return and there are no bubbles then the next thing to check is the injection pump itself although problems there are unlikely.