Yanmar Trouble Again

[Quietly_Making_Noise]

Last year we rebuilt half of our yanmar 2qm15. We were experiencing loss of power (thought to be because of a leaking head gasket) and were also having difficulty with air entering the fuel system. After the rebuild (Replaced head gasket, head resurfaced, valves replaced, new injectors, ect. ) the engine ran beautifully. I was able to reach hull speed at 80 %. This of course was just in time for the winter. About 6 months later the problem returned. I am lucky to get half the speed at 80%. Filters fine, fuel stable, air filter clean, mixing elbow clean. This leads me to the two Items I did not mess with. Lift pump and injection pump. I have also recently discoved a small amount of fuel seeping from the nut on the discharge side of the injection pump just before the hp line. Today I removed this nut and found a small oring on the threads. Could this o-ring be causing the problem? I am also considering pulling the pump and taking it somewhere for testing. It looks as though there are 4 bolts holding it to the engine. Is this an easy item to remove and is there anything I need to worry about disturbing? Any advice would be greatly appreciated.

 

[Bill Roosa]

Panic FIRST

OK we got that over with now we can turn to the problem with a clear head.The facts. It ran great a short while ago, you waited a while and now it does the same thing it used to.
your discovery of a fuel leak is probably the problem. Injector pumps don't go bad that often but and lift pumps either work or not. A small leak on the output side of the injector pump would allow air in after you shut down the engine.
Before you go rebuilding the engine replace the O-rings on all the injector output lines.

 

[Warren Milberg]

I'd also suggest checking/replacing all the crush washers on the injectors.

 

[Ray Bowles]

Is the bottom of the boat clean and the prop clean?
Ray

 

[Quietly_Making_Noise]

Thanks for the replys. The brainstorming on this forum has helped me solve most of the problems I have had on my boat. Crush washers were replaced during the rebuild and I have wrapped all fittings with toilet paper and ran her against the dock to check for leaks. The only one appears to be the one from under that large hollow nut on the discharge side of the pump. I pulled the oring and found a small nick in the rubber. I will have to replace both. I just cant believe that this would cause this much of a problem since there is not suction on that side of the pump. The bottom and prop were clean when the problem started, but I will have to clean them again before the test run. Thanks for the suggestions.

 

[DougM]

Check your fuel hoses as well. as they age. they can develop superficial cracks which under running conditions can allow some air into the fuel system. Relatively easy to remedy, just replace the lines.

 

[Ray Bowles]

Quietly, It is also possible that either a chunk of dirt of that small piece of rubber from that O-ring could be blocking the injector. If its now that hard I would pull the injectors for a look.
Actually I'd just flatly pull the injectors for a look and see if you have even color on both. A difference in appearences will tell which cylinder is weak.
Ray