Yanmar 3GM Dies When Trying For Max Power

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robbieg

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Got a newly rebuilt 3GM30F which has been starting and running fine. Got about 20 hours on now since the rebuild. Boat and prop are clean and misalignment shouldn't be a problem. No problem with the throttle linkage. Same prop we have always had so shouldn't be overpropped.

Yesterday I had her running for about 2 hours at 2500 to 3000rpm-all was well with no smoke and clear water out of the exhaust and good boat speed. I then tried to push the revs up to see if she would get to her rated max rpm of 3600. Pushed the throttle wide open. She got to about 3200rpm held it for a few seconds but sounded "bogged down" and then the revs died away and she stopped. No material black smoke whilst this happened

Restarted straight away at tickover and for a few second she threw out black water and a little smoke which cleared. She then ran at 2500rpm to 2900rpm on way back-clear water no smoke and no sign of an issue. When tied up I ran her up to 3600rpm in neutral for a moment before idling her for a couple of mins and shutting down.

My first thought was fuel starvation but if so would there have been all the unburnt fuel in the exhaust following restart? Normal airfilter set up and can't see any blockages etc so surprised if air starvation the problem. Will check the exhaust mixing elbow but would be suprised if this had coked up in the few hours she has run since rebuild.

Anyone any other ideas?
TIA
 
I would suspect the exhaust elbow - did you remove and clean it out when the engine was reconditioned? This happened on a Perkins Perama I had a few years ago admittedly with more hours. Also check to see if you have any air leaks in your fuel piping. I had this problem when I fitted a new engine complete with new fuel system. Turned out to be an air leak through one of the unions - tightened all fuel unions and had no problems since.
Hope this helps.
 
Sounds like fuel starvation. If so there will be NO unburnt fuel in the exhaust.

If it was air starvation the engine will not die AND you will get copious amounts of dark smaoke from the exhaust.

I would start by checking your fuel filters. [Occams razor]

However on reflection it is a little odd that the engine stops and then restarts easily. Usually it would just slow down.
 
Had exactly the same symptoms on a Yanmar 4JH.

Cause was secondary filter.

I'm with TQA & Occam on this one: check your filters.
 
Fuel Starvation

Yes I would have said fuel starvation but rather thrown by the jet black exhaust water on restart and the ease with which it restarted which seems to suggest overfueling. And I can't see why air starvation should be a problem since a similar engine in the same space was fine but if it were the issue I would have expected some black smoke before she died. All rather contradictory symptoms!

Plan so far is to bypass the fuel tank and primary filter with a jerry can to check the fuel starvation problem and then take off the air clearner cover to check the air starvation theory.However any further ideas gratefully received....
 
My thoughts are much as the others have suggested. It sounds very much like a filter problem. When I experienced it at its worst it was diesel bug. Engine died completely under power but would tick over fine. It was dark so I don't know about smoke colour but a bit of black on starting could be due to all sorts of factors and I wouldn't let that influence disgnosis too much.
 
Please check for a fuel supply hose has not collapsed with age or excessive vacuum . The inner liner in rubber type hoses has been known to collapse with age and cause a perfectly good looking hose to not let fuel flow..
 
whats happening when out of gear when the throttle is increased to full, you should hear the overspeed limiter cutting in. It could be that needs adjustment ?, not sure how much you had apart.

Steve
 
Similar problems with a 2gm going up the Thames estuary 3 years ago - not the best place for it to happen with a 4 knot tide sweeping you in!
I thought it was fuel related and subsequently methodically worked through the filters and cleaned/replaced everything. There was some improvement but.............. Anyway I replaced the air filter and hey! Back to normal. I now replace the air filter EVERY year.
 
you are supposed to wash it in detergent every 250 hours, or until it disintergrates which could be sooner if it gets diesel back from the intake valves which does happen.

cooker hood foam is a good replacement but must be non charcoal impregnated and must be stuck only with glue on the metal mesh.

Steve
 
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