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Old 11-26-2016, 01:51 PM   #1
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Question Onan Generator Problem

Hi Folks. I have a 2015 Jayco Precept 31U that,s been pretty good to us over the last two years ... except for the Onan 5.5K gasoline generator. We have maintained our generator per the maintenance instructions by running it with a 50% load every month and changing oil and filter at the first 50 hours. We have actually used the generator only five - six times, and it has shut itself down every time with a code 14 (over frequency) alert.
Following the first failure last year, we immediately took the unit to the nearest Cummins Service facility where they kept it for three weeks in an attempt to reproduce the problem. They eventually did reproduce the failure and replaced the carburetor under warranty.
This year the first time we used the generator, it ran fine for 2 1/2 days then shut down with the same error code. Then it failed after only 6 hours of running, then 3, then 1. Now the generator fails after 2 -3 minutes of running with no electrical load whatsoever, each time with the same over frequency code. The Cummins repair facility experts are stumped except to state that the generator is no longer under warranty. They cannot get the generator to run more than 3 - 4 minutes, even tough it starts without hesitation and the error is always the same.
While I continually work with the cooperative Cummins staff I was just wondering, has anyone else out there in the RV community run into a similar problem? Was there a solid solution?
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Old 11-26-2016, 02:09 PM   #2
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I had a similar problem about 3 years ago. I finally went to a Onan authorized repair Depot in Yuma AZ were the repairman was a expert on generators. They tried a new carb first around $200 that did not completely cure it. They finally replaced a control module about $140 as I recall. That is what fixed it.
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Old 11-26-2016, 02:26 PM   #3
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An over frequency error is from an over speed condition on the engine.

The engine need to turn a specific speed to create 60 ( Hz ) cycle per second. If it runs too fast, it goes over 60 Hz.

What ever controls the throttle movement on the carb has to be the problem.

The old engines used a fly weight governor but many new ones use a electric speed control ( a small electric motor ) controlled by electronic circuits.

Odd that they don't suspect this.
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Old 11-26-2016, 07:58 PM   #4
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twinboat of course has the answer... I'm going to venture into the fact that the local Cummins shop doesn't have the technical ability to understand what's going on... and since most of these don't have a "data link" for a computer to test and diagnosis the problem they are lost..

that said... I was taught to understand the theory, than test and diagnosis why it's not working as described... my only suggestion is to find a guy who knows how to do this...
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Old 11-26-2016, 08:50 PM   #5
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I have had the same problem on both an Onan 5.5 and a Generad 4.0. Over speeding was the cause on both. No one has mentioned anything about ethanol but I know for a fact that both units had carb. problems which was caused by ethanol. The pot metal small carbs are made from will react quickly in a bad way due to the effects of ethanol. I deal with small engines on a large basis and ethanol will be the death of small engines and that is only increased by the the corn bunch pushing E-15 down our throats. The over speeding with the ethanol problem carbs is caused by the governor trying to get the engine up to speed and going from to slow to to fast. I don't doubt that a controller could cause the problem but I will tell you that if you don't do something about the ethanol in your gasoline generator that sits idle for any length of time you too will have trouble. Before you put it away for more that a couple of weeks install a fuel shut off and run the carb. as dry as possible. I went a step more and installed a second tank for the generator and only use aviation gas when I can't get ethanol free. Cleaning a ethanol stopped carb. will convince you.
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Old 11-27-2016, 08:07 AM   #6
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Thanks

Thank you to all who have responded. I am tending to think that this will eventually lead to the control module, and I will certainly suggest it to the Cummings Repair facility mechanics.
The ethanol issue is also very valid, but I religiously run the generator every two weeks during the summer months, and once per month plus constant Stabul fuel stabilizer during the winter months. It doesn't seem to be a problem with the engine starting or running but, rather, engine shut-down due to over-speed/over frequency.
The lack of electronic diagnosis by the Cummings team also seems probable.
Your feedback has been great and I will post once the solution finally exposed.
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Old 11-27-2016, 08:22 AM   #7
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exactly right, first the carb then the control module! Don't fool with it, just replace the module, they should have already done that!

onan carbs are notorious for failure due to non use. Best thing to do is keep a spare and rebuild, blow out the jets of the stored one. Jet's plug up so easy on those things. Best way to deal with it is to put a drain in the float bowl and drain it when you store it. No fuel, no pluged up carb!



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Originally Posted by mhbell View Post
I had a similar problem about 3 years ago. I finally went to a Onan authorized repair Depot in Yuma AZ were the repairman was a expert on generators. They tried a new carb first around $200 that did not completely cure it. They finally replaced a control module about $140 as I recall. That is what fixed it.
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Old 11-27-2016, 10:33 AM   #8
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I would be arguing that since you brought this problem to them under warranty and they failed to fix it that it is still under warranty.
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Old 11-27-2016, 10:42 AM   #9
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how old is your gas?
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Old 11-27-2016, 11:17 AM   #10
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ONAN

I have a dumb questionWhere is the physical location of the starter in the gen box? 7.5 ONAN HDKAJ 11451 ser H. I'm cramped under there but can slide unit around some. Just need to take off the left or right side panel for access to the starter. 2005 Fleetwood, Expedition.
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