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Old 06-03-2017, 06:36 PM   #1
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Onan 4K generator shuts off

Helped a friend check out his 5 year old onan 4K generator. It has low hours less then 100 for sure. He has been dealing with this problem for over a year. It starts easily but won't take much load. It will run with a light load less then 10 amps for a good while. I put a larger load on it the microwave and the a/c unit which brought the amps too 23 amps and 115 volts and in a minute it shut off. The generator is rated for 33amps so it should have kept running. The fault code showed #38 which is an excessive load code. Any ideas is there anyway to set the point at which it shuts down at 30 amps rather then 20? I plan on checking the fuel pressure at the carburetor under load but I doubt it will be a problem. This is a 4 lb pump I presume as all onan pumps that I remember for many years are 4 lb.
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Old 06-03-2017, 06:52 PM   #2
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My first thought would... are the batteries fully charged? The converter could be doing a charge and drawing 10 to 14 amps by itself. Next I would say if you have a volt meter with a load clam... open the breaker panel and check the hot leg coming into the main to see what actual load is being pulled on the 120. Beyond that, is the RPM dropping with the larger load? The RPM should maintain or even step up when the load is applied. If it is not sensing the larger load and stepping up the motor it could very well be an excessive load as the gen is not putting out enough for demand.
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Old 06-03-2017, 07:24 PM   #3
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Battery should be up as it is in a garage and was plugged in . To run the generator the shore power is unplugged and then plugged into the generator plug. The clamp on amprobe is on the power cord showing power amps from generator ?my fluke is checking the volts at a plug.The generator sounds like it is lugging down under the 22 amp load is this normal? If the generator was rotating too slow wouldn't the volts be low? Do I need to put a frequency meter on it also to see if it is not rotating fast enough? Not used to these inverter type generators my old 1976 Onan used to speed up under load.
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Old 06-03-2017, 07:37 PM   #4
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Based on what you are saying I am going to go with gen is not stepping up. Open the housing and get to the carb. Try manually pushing up the throttle to raise the RPM hold it there and apply the load and see if the situation changes.
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Old 06-03-2017, 08:33 PM   #5
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I can try that when I get back too his house. If I bump up the throttle will the voltage go up accordingly like on the older type generators? Not good. If this helps does it mean there is a carburetor problem or something else ? Is it possible I could increase the throttle too much or do I just try to keep it from not bogging down?
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Old 06-03-2017, 08:50 PM   #6
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You can check the voltage with your meter. It should maintain. The object here is to not really bump up the RPM much but more maintain the same under load. When the load hits the gen you should hear it. Like if you have a riding mower when you start the mower deck. Think of it like going up a steep hill with your car. The throttle gets pushed down more, pushing more fuel into the chamber which creates a bigger explosion and delivering more power but the RPM does not actually go up. Then as you reach the max for the engine and it can not develop more power the RPM will drop and then the gear changes and the RPM goes back up...and the cycle starts over.

As for if this "fixes" the issue, then you have to start digging into the how and why for that model. But at least you will know what is happening.
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Old 06-03-2017, 11:04 PM   #7
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I'll give it a try in the next day or two thanks
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