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Old 25-06-2013, 21:18   #1
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Inscrutable Genset Problem

I have a 9kW Onan genset with less than 100 hours. Its in the lazarette of a motor yacht. Filter is a Racor 1000.it shares a fuel pickup with a larger genset, with which there are no issues. Genset is about 25 feet from the tank.
Genset runs perfectly but it stops whenever I walk in the aft head, about 6 feet from the genset but on the other side of bulkhead. Then it will not restart. Fuel hoses run through the side, behind a cabinet. Its not that i am walking on the hoses and pinching them off. The diagnostic error code is fuel starvation.
I replaced the filter. Tank has been throughly cleaned and looks spotless. Diesel is new. As I said, the other genset has no problems with that pickup, nor does the starboard engine.
Boat is 75' so I am not unduly tilting the boat.
My solution is to install a booster electric pump. Who knows if it will work. Any ideas as to what causes the problem?
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Old 25-06-2013, 21:27   #2
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Re: Inscrutable genset problem

If the only thing you are doing by walking into the aft head is slightly changing the heel of the boat try adding some fuel to the tank. If that fixes the problem then suspect a pin hole in the vertical pick-up tube.

Explanation:

A slight change in heel puts the pin hole above the fuel level and allows air to get into the line. The bigger gen set is able to over come this small amount of air but the smaller one cannot.

Another really far out possibility:

Are you wearing a smart phone on your person? If so, the phone may be pulsing and causing problems with the electronics of the gen set. If so, there may be nothing wrong other than the gen set control system just thinks there is a problem. Pull the battery from the phone to verify.
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Old 25-06-2013, 21:37   #3
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Good thinking, but added 400 gallons and made no difference. No smart phone issue, its fuel starvation. When it happens I check the Racor and its not full of fuel
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Old 25-06-2013, 21:48   #4
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Re: Inscrutable genset problem

Maybe with a 25 ft run, ya might need a larger Dia fuel line ! but I would think a fuel pump would be a better idea ! At least thats what I would do.
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Old 25-06-2013, 21:57   #5
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Re: Inscrutable genset problem

Quote:
Originally Posted by dohenyboy View Post
Good thinking, but added 400 gallons and made no difference. No smart phone issue, its fuel starvation. When it happens I check the Racor and its not full of fuel
Then that almost certainly proves it is an air leak between the tank and the Racor (or in the Racor itself). In order for fuel to be removed from the Racor it has to be replaced with air from somewhere. Find where the air is coming from and your problem will likely be solved.
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Old 26-06-2013, 05:55   #6
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Re: Inscrutable genset problem

And...vacuum leaks are a bear to locate. Suggest using a radiator/cooling system tester to provide very low pressure to the system and then go over the system with a bright light and soap solution at every joint and every inch of any hose.
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Old 26-06-2013, 06:03   #7
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Re: Inscrutable genset problem

Final test - temporarily feed the genny with a jerry-can of clean diesel on deck. If the genny runs without a hiccup.... then the problem's gotta be somewhere in the fuel system.
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Old 26-06-2013, 06:21   #8
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Re: Inscrutable genset problem

A major clue may be how and when does the genset restart?

Another question is the relative height of the fuel in the tank, the top of the filter, and the fuel inlet on the genset itself. If the fuel flows by gravity from the tank to the filter to the genset, you may have a clogged line. If it has to go uphill, it is more likely a pinhole letting air in.
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Old 26-06-2013, 07:15   #9
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Re: Inscrutable Genset Problem

I would not put a supplemental fuel pump until I was sure the fuel line was perfect. diesel sure smells up a boat.
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Old 19-05-2014, 18:18   #10
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Re: Inscrutable Genset Problem

Update on the problem
The 30 feet of fuel hose from the tank was plugged. I replaced the hose, and that solved the problem for a while. Finally had to have the tank cleaned. I had been told that it had been scrubbed spotlessly clean but was not the case. Tools, old bilge pads etc and other gunk and dirt were found within the tank.
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Old 19-05-2014, 19:44   #11
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Re: Inscrutable Genset Problem

Thanks for the final (?) update... very interesting! That's a lot of crap for a spotlessly clean tank. Still not sure how your walking into the head caused the problem, but glad that it is solved.

Cheers,

Jim
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