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Old 12-06-2017, 03:48   #1
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Generator failure

I have an Onan MDKAV 7.5kw 50hz which has served well over 14 years with relatively low usage (est. 2,500 hrs) and it now does not start. I know about Onan coding but the signal I get is green and yellow flashing together repeatedly - no coding. The problem began occasionally with the motor running well when it did start but now nothing at all. Can anyone help please?
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Old 12-06-2017, 05:03   #2
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Re: Generator failure

I can't interpret your question, yet. Do you mean only the generator has failed? Or do you mean the (diesel?) engine won't start/run? Or...?

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Old 12-06-2017, 05:07   #3
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Re: Generator failure

And if the engine doesn't run, does it at least crank?
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Old 12-06-2017, 06:01   #4
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Re: Generator failure

If it is the drive motor, when was the last time the valve clearances were set? You might find that re-setting the valves to the proper clearances solves the problem.

FWIW...
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Old 12-06-2017, 06:17   #5
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Re: Generator failure

Thanks for your responses. I should have said clearly that the problem related only to the generator and the 'motor running well when it did start' meant the generator motor (which is Kubota 3 cy diesel) and not the boat drive engine. No attempt at cranking now - when it did crank (before complete failure), it always started immediately - always has. The primer (lower part of switch) works the fuel pump or sounds as if it does. (New fuel pump 20 hours ago.)
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Old 12-06-2017, 07:15   #6
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Re: Generator failure

So it's the generator motor that's the problem, and it now doesn't start, yes?

Often fuel or air, but first... do you have electrical power to the starter? Click? Or nothing? Could be something as simple as a loose electrical, perhaps ground, connection.

I'd say check and report on that first before everyone has to go down the fuel or air rabbit holes...

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Old 12-06-2017, 08:27   #7
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Re: Generator failure

If the preheat function works, my bet is on the signal wire to the starter solenoid coming loose.
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Old 12-06-2017, 23:18   #8
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Re: Generator failure

I'm really not following your description of the symptoms.

Does it not crank at all? And if it doesn't crank, does it make any sounds when you attempt to crank it?

Or does it crank but not start running?

BTW, be careful about over cranking and flooding the muffler and subsequently the engine. Then you will have a big problem.
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Old 13-06-2017, 00:03   #9
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Re: Generator failure

Know nothing specific about your genset, but the gradual onset of the problem suggests an electrical connection problem, more likely a corrosion-related ground issue than a positive side one, a mal- or non-functioning sensor issue, or a computer (chip/pc board) gremlin.


Start with the easiest/cheapest first (checking/verifying connections), move to process of elimination on sensors, senders and switches, and unless you're an electronics person, call in a technician for computer issues beyond simple replacement...


Perhaps someone with info specific to your genset will pop up though...
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Old 13-06-2017, 01:10   #10
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Re: Generator failure

Thanks, Tanglewood. The generator now does not try to start at all. the problem grew over two weeks. first it was occasional not trying to start but increasingly frequently it did not try until now when it does not try at all. I think Jimbunyard may well be right that it is an electrical connection problem, possibly corrosion related - maybe the connection to the starter solenoid as Sailmronkey suggests. I have gone around the sensors but they are either new or test OK. Thank you all for the useful guidance; i just hope it is not the control panel !
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Old 13-06-2017, 04:54   #11
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Re: Generator failure

If the engine started and ran as long as you held down the start switch then stopped when you let it up it's possible your brushes are bad. My mdkau 5kw did this when my brushes went bad at about 2450 hours. The computer shuts down the engine if it doesn't see 120V on mine and probably 240v on yours which it can't generate if the brushes are bad. Excessive cranking may have compounded the problem by causing a hydrolock.
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