yanmar 4jh4 hte fuel issues

[nuance]

hi,
engine is newish, 600 hrs. over last season saw a gradual reduction in max available revs to 1600, either in neutral or under load. have just launched for season. Engine starts easy in tick over, runs smooth with no black or white smoke, but stops after 5 or 6 seconds, or when I try to apply revs. have cleaned / replaced primary and secondary filters, and hoses from tank to engine. have rigged a day tank with fresh today diesel and primed per the manual.

My thinking is symptoms point to fuel starvation. Also the fact that she starts and runs for a few secs implies that pump and injectors are OK? So I'm thinking air is getting in somehow, somewhere. any suggestions as to how and where to look for issues will be much appreciated.

thanks

N

[Bluewatercruise]

Hi
I've got the same engine with the same problem. It finally got sorted today. My problem was dirty fuel and finally air leak combining to cause the issue. It sounds like you are a long way along so I'll tell you what I went through and it may trigger something you can fix.
I kept saturating fuel filters after a bad fuel top up. I treated the fuel so the bacteria died and settled to the bottom of the tank making things better and worse. I rigged a home made polishing system that partially cleaned the diesel. I kept saturating filters. (A racor and the pre-injector filter).
I finally coughed up and got the fuel professionally polished- the home made rig was useless in comparison. I also opted to put two racors in front of the pre injector filter. I also replaced the hose back to the tank like you have. I then had clean fuel and the same problem you've described. I found a micro fracture in the metallic fuel hose connection at the filter end, no doubt a vibration/fatigue issue that I never thought possible.
Finally I changed and changed again the o rings and cartridges on all filters and completely reprimed everything repeatedly.
It sounds as though you've done all this but all I can add is that you may think you've addressed something but go back and check it all again.
Best of luck.

[nuance]

thanks Bluewater. I've got the fuel pump off and it's being professionally serviced / cleaned etc. going back on tomorrow. I hope that works as GBP 350 cost!

If not I'll get on with the cleansing process you describe.

N