Yanmar 3JH3E Max 2500 rpm

[skipperpete]

Originally Posted by sinnerman

If no fuel is coming out of the injection tube when it is disconnected from the injector, then you most likely have a stuck piston (plunger) in the fuel injection pump. This is usually caused by water in the fuel getting into the pump, sitting there, then corroding (rust) the metal piston.


You can try taping the injector pump with a screwdriver handle or plastic mallet with the engine running to see if it frees up.


Another option is to have an engine mechanic remove the delivery valve (threaded fitting where the injector tube attaches to the pump) from the top for that cylinder which is not working, and pour some penetrating oil into the plunger cylinder to break up the rust. See pic. Yellow is the plunger/piston...
(The other parts sitting on top of the piston are the delivery (check) valve which traps the fuel in the injector line aft er the injector fires...)


Cheers

Sinnerman, almost all of what you posted other than the pump diagram and the fact that wet fuel oil will cause injector pump plungers to seize or stick … is contrary to what every diesel mechanic learns and knows by heart. When a plunger in that type of injector pump sticks or seizes, the neighboring plungers are all locked in rotational position by the fuel rack and the engine response to this is
1. An uncontrolled overspeed
2. No response to the stop control lever OR GOVERNOR
3. No ability to un seize a stuck plunger, replacing is the only option (unless you happen to be at Chagos and really need to get the engine running as a matter of survival)
The final response to a seized plunger is the lucky one, the engine simply won’t start. But since most in line injector pumps go to full fuel rack position after shutdown the odds are heavily in favour of the overspeed.
Removing the delivery valve is something we do regularly to accurately adjust injection timing but no sensible repair of a plunger can be undertaken by doing this, and no amount of soaking with penetrating oil will dissolve corrosion between the astonishingly delicate surfaces of the plunger and barrel.
There is a situation where the gums and waxes in fuel oil can cause a plunger to stick and I’ve experimented with freeing them up by boiling em in fuel oil to no avail.

[Icarus]

Originally Posted by Frk. Jensen

My 3JH3E engine from 2001 (1400+ hours) suddenly wont go above approximately 2500rpm under load. While not in gear there are no problems reaching higher rpms.
I normally run at about 2300rpm and do feel speed is as it has always been. Also throttle handle is at usual position. It's just like nothing happen when pushing it beyond the 2500rpm

Boat has just been on land, so everything is clean on bottom and propeller. All filters have been replaced either this year or last year

My guess is that it relates to fuel pipes somehow? What's the best approach to debug that?

I feel the engine sounds like allways, but think I read somewhere that it could be difficult to hear if one cylinder wasn't working. Any comments on that?

Possibly a fuel problem
Clogged filter, injectors
Weak fuel pump
Air entering the fuel supply..micro air bubbles on the suction side
Timing changed, lose injector pump...unlikely
Accelerator cable, linkage?