Onan 4000 Generator Problems

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kbfeip

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Joined
Dec 24, 2006
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148
Location
Discovery Bay, CA
My Father In Law has constant problems with his Onan with less than 200 hours on it.  About 90% of the time It will run for for a period of time between 5 and 20 minutes, and then simply shuts down.  He has done the following:

Changed oil with Onan brand oil, new spark plug, new fuel filter and new fuel line from fuel filter to carb, new air cleaner, and checked exhaust and spark arrestor for clogs. 

It doesn't sound as though it's a fuel related issue, as when it quits, it shuts down immediately with no sputtering, just as if you had turned the switch off.

The unit will restart immediately without problem, and sometimes run forever, or sometimes repeat the short run problem.

The Onan rep in Phoenix could not figure out the problem.  Oil level has been check repeatedly, no foaming of the oil is present.  Whenever the generator is unplugged from the RV and running without load, the problem does not occur.

Anyone with some magic suggestions that we might check out in between card games?



 

John From Detroit

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Apr 12, 2005
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24,782
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Davison Michigan
One possible cause is a short/loose connection in the ignition/control system,  Could be sending a "STOP" signal when you are not pressing the STOP button

Inspect all wiring and connections on the control side
 

Dan Walters

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Jun 15, 2006
Posts
485
Location
Bellville, Texas
I have an Onan 4000 in my coach and had a similar problem with it shutting down after a short run.  It turned out to be a battery problem, not a problem with the genset.  I replaced the chassis  battery and the 2 house batteries and have not had any problems with it since.  It will run for hours on end now without a hitch.  Some coaches use the chassis battery to start the genset and some use the house batteries so it could be a problem with either one.  Mine uses the house batteries.  As John said, it could also be a short or loose connection in the wiring circuit as well.

Dan
 

Howard R

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May 3, 2005
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567
Location
Minnesota
kbfeip said:
My Father In Law has constant problems with his Onan with less than 200 hours on it.  About 90% of the time It will run for for a period of time between 5 and 20 minutes, and then simply shuts down. 

While the odds are slim that you would have the same problem, for what it's worth.

My Onan 4KW started getting intermittent, ran fine most of the time, starting shutting down on the road.  Anyway, long story short it finally quit one hot day going through Lincoln NE.  I don't have the rig here now to look at so can't be as specific as I w would like.  However, with the access door open, cover off the generator as you look at it there is a ground wire attached to the face of the generator ... believe it is a 7  mm screw.  Screw was stripped, ran a tap through hole on generator and replaced the screw and all was well.

If you have trouble finding it, let me know and I can go and take a picture.

Like I say, may not be your problem but it acted much as you describe.

Howard
 

alstack

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Joined
Nov 6, 2007
Posts
1
I'm posting this here because I'm not sure where else to start. We just purchased a 1987 Honey with a 4kw Onan that is permanently mounted and gets its gasoline from the vehicle gas tank. I asked the previous owner if the generator would start and he said he wasn't sure but he wouldn't start it without cleaning the carburetor out first. I opened the door and took a quick look at the unit tonight and I don't readily see what looks like a float bowl. Is there one? Should I not in fact try to start this unit before doing some kind of maintenance? Is there a better place to go to find info on this unit?

Alan S.
 

Karl

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Mar 3, 2005
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Elkhart Lake, WI for the summer. Work at Road Amer
The unit may be damaged, and that's why he's reluctant to try and start it.  I would suggest checking the oil first, and replace it and the filter if it looks dirty or milky. Disconnect the spark plug and try pulling it through with the rope starter, if it has one. It should pull though fairly easily. If not, chances are it has internal damage or is frozen up due to corrosion or lack of oil. If all feels and sounds o.k., go ahead and try the electric starter, listening for any signs of internal damage. If you can't pull it through or crank it over with the electric starter, it's time to go back to the seller with your complaint. If everything seems o.k. and it still won't start (don't forget to re-connect the plug wire), the fuel may be too old or there may be water in the carburetor. Yes, there is a float bowl, and it will be near the bottom of the carb., right after the air filter. You may need to remove the air filter housing to get to it. There will also be a fuel filter that may have become clogged. Check it and replace if necessary. Actually, it's a good idea to replace the oil and all the filters anyway since the previous owner doesn't know if it will run, and it probably hasn't for some time.

Good luck! :)
 

Gary RV_Wizard

Site Team
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Feb 2, 2005
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73,489
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At our Silver Springs FL home
Adding to Karl's excellent advice, it is quite common for generators that haven't been run much to be difficult or impossible to start without a carb rebuild.  It is also quite possible that the electrical generation portion has failed due to moisture (condensation) build-up internally and that is a very expensive repair. The traditional wisdom is that RV generators need to be exercised (run under an substantial electrical load) at least once a month to keep them functional.

In short, don't buy an generator that isn't running.
 

Clay L

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May 28, 2005
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1,725
Location
X Full Timer Now Palisade CO
There are a number of things that can cause the intermittent problem you described but one thing is air getting into the fuel line. Sometimes mine would run for 3 or 4 hours and sometimes for a few minutes. It didn't sputter when it died.
Mine had a loose clamp where the fuel line transitioned from rubber to metal close to the gas tank. One RV dealer and one Cummins shop failed to fix it. Both thought the fuel pump was bad and replaced it.
A tech at the Winnebago factory finally found the real problem.

It did throw a light code indicating a fuel problem when it died.
 

Lowell

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Aug 15, 2005
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2,221
Location
Tempe, AZ
RV Roamer said:
The traditional wisdom is that RV generators need to be exercised (run under an substantial electrical load) at least once a month to keep them functional.
/quote


What would be considered a substantial load for a 4000 watt generator that is being exercised?
 

geraldt15

New member
Joined
Jul 26, 2013
Posts
1
John From Detroit said:
One possible cause is a short/loose connection in the ignition/control system,  Could be sending a "STOP" signal when you are not pressing the STOP button

Inspect all wiring and connections on the control side

My Onan 4000 watt Gen. started shutting down after about one to two hours after running even in cool weather. I completed all services required and problem persisted, upon further inspection I found a mouse had made a nest inside the housing obstructing air flow/cooling. This caused the generator to shut down to prevent overheating. suggest always checking for this after camping in wooded areas. 
 
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