Help! diesel engine gremlin

[jmp]

I have a Vetus M 3.10 aux in my boat. It is a 3 cyl marinised Mitsubishi about 950cc. The same unit I beleive is badged by Beta, Nanni etc The unit ran 200 hours Last season, and about 50 so far this.It is old, but in all general areas in good order.

Without apparent reason the engine loses power and revs drop from 2000 to 1000 or so .It is as if the prop has become fouled .After some time the revs return to normal; so far without stopping completely.I have tried engaging sterngear etc to no avail,in case of fouling ,and have now checked physically the prop &shaft.

Last season this may have happened once or twice,but was quickly over and thought to be an innadvertant nudge of the lever with a foot .

This season there is a definite intermittent recurrence which is most alarming .
Filters etc were renewed as normal,and the injectors serviced at the start of the season .

Any suggestions would be greatly appreciated.

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[tony_brighton]

sounds like fuel starvation somewhere.

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[duncan]

I would start with the fuel filters - a lot can happen in 4 - 5 months.

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[mtb]

I agree with the others .
Is the tank breather ok as a vacuume may cause partial fuel problems.
Try opening the tank filler to see if it helps !!.
Might be a sticking pump but things like this can be hard to pin down .

Cheers
Mick


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[Heckler]

do it logically instead of just guessing
when revs drop do you get black smoke out of exhaust?, if you do something is loading the engine, ie, prop shaft or prop binding, gearbox tightening, engine siezing? very unlikely but methodically.
if not above only thing that can cause engine to slow is lack of fuel or air, lack of air will cause black smoke also, lack of fuel will be noticed by among other things quietening of exhaust, lack of fuel caused by blocked fuel filters, start with stack pipe in tank, then pre fuel filter, then fuel filter, check breather is open in fuel tank to let air in as fuel is used, check lift pump is operative, has diaphragm got small hole in?
if all ok then gets down to is injector pump and governor doing its job?
take it step by step witht the simplest things first, best of luck
stu

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[paulrossall]

I agree with sonny-lass. Check your big pre-filter, on my boat it is a CAV filter. This is the main filter which gets rid of any crap which is in the diesel. Too many boaters put cheap farmers diesel in their boats without proper filters and wonder why they have a problem.
After that check for air leaks. Again check that the breather pipe is functional.
If this does not solve the problem report back and we will offer other sugestions.
Hope this helps.
Paul

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[andy_wilson]

Most likely cause.

Air leak in suction side of fuel supply.

A typical system will be gravity fed from tank to pre-filter. My tank feed is from the top meaning it syphons under pressure provided the tank is half full.

Beyond the pre-filter the lift pump sucks the fuel and a minor air leak will cause exactly the symptoms you describe. The leak is sometimes evidenced by a minute leak when the engine is off, but not always.

Air sucked in thus will be self bled (as the engine faulters) provided your injector pump can cope with it.

Gently check and tighten all the system connectors (say 1/4 turn max unless totally slack) and try again.

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[charles_reed]

Obviously occasional fuel starvation - could be a faulty pump but most likely a minute air-leak which only occurs occasionally.

It sounds like a very similar problem to one I had which took me nearly a year to solve and which gradually got worse until I had to tie up under sail in Ribadeo.

It was traced to a perished washer in the on/off tap in the diesel feed line, allowing air into the system when the level in the tank fell below the pump level (which meant about 1/2 full).

I only found it in the end because I stripped the whole fuel line from pick-up in the tank to the pump, under the impression that it was due to dirt in the line.
There you go - serendipity sometimes occurs with boats.



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[oldharry]

Agree with Charles and the others - fuel starvation either from a blockage, or a minute air leak. Blockage can be anywhere including the air vent to the fuel tank, while the minute air leak is most likely to be between the fuel lift pump and the main injector pump. Look for traces of diesel at each connection. Consider too that there may be a pinhole leak in the lift pump diaphram - which will of course get worse.

Minute air bubbles will pass through the injection system without actually stopping the engine, but will reduce the amount of fuel being delivered, thus slowing down the engine. As it slows down the amount of air being drawn in reduces so the engine picks up again - Until there is enough air in the system to slow it down again....

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[jmp]

Thanks everyone who has or may respond.
I have done enough stabbing at possible causes.It is clear from the feedback that I have a busy weekend.
A full systematic check from the tank onwards is the way forward.

Thanks again .

Michael



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