I was exercising my ONAN 4000 the other day as I do monthly and after about 45 minutes it just shut down. It re-started after a couple of minutes, again after 30-45 minutes before shutting down again. One more time before I decided there was a problem. I pulled it out of storage this afternoon and checked the oil level and quality and it was fine.Started it again and boom same thing. I didn’t have the sequence of how to get the trouble code with me so I backed it back in to storage.I use a fuel stabilizer and premium fuel for the genset at all times.I will try to get the code on Saturday but is there anything else I could check when I have it pulled out?It seemed kind of hot in the compartment but it was only about 75 degrees today and we’ve run the genset in 95-degree weather with no problem.MOD: 4KYFA26100KSER: H050816555SPEC: K

My opinion. You may have a fuel pump getting weak.

Even though you have checked the oil level, if your Onan has an oil level switch it could be bad. Can you tell if oil is foaming? This could also cause oil level or oil pressure switch to shut it down.Along with "whemme" post the fuel pump could be sucking air through decaying rubber line.

Check the air filter, fuel lines (as stated above).Have you changed gas cap? Sound like you are sucking fuel from the tank, but the used gas is not being replaced by air (tank sealed to tight)Loosen the gas cap and see how long it runs.

Have you had a tuneup done? There could be crud in the carburetor. Also, if you can get ethanol free gas it would be help. Small engines don't get along with either.

TexasUltra wrote:I use a fuel stabilizer and premium fuel for the genset at all times.So called "premium" fuel is a waste of money in a generator......and anything else that doesn't specifically require it.Your symptoms sound a LOT like mine when the fuel pump failed.It would start and run fine......until it got hot, it seemed.

ONAN runs, stops, starts again | Good Sam Community

TexasUltra
Explorer
Jul 13, 2018
Thanks, everyone for the help, advice and a little humor thrown in. It was the fuel pump ($59)
Sam_Spade
Explorer
Mar 26, 2018
ernie1 wrote:
but when shut off I'd still get a strong odor of gasoline.

And regardless of other symptoms, you didn't think THAT was something that should be investigated and fixed ??
I certainly DO.
ernie1
Explorer
Mar 26, 2018
On my Onan 2800 it would quit running after it had run for maybe an hour or so, less if it was really hot out and more if it wasn't. After it would quit running I'd get a real strong odor of gasoline for a few hours. If I removed the front panel the generator would run continuously non stop but when shut off I'd still get a strong odor of gasoline. Seems like it must have been overheating and that the problem was not the fuel pump.
TexasUltra
Explorer
Mar 26, 2018
marcsbigfoot20b27 wrote:
You should not run the gen with the generator panel open for more than a few minutes. Air cooling won’t work correctly.

Just for the record only the trailer access door was open, not the GenSet service door.
j-d
Explorer II
Mar 25, 2018
TexasUltra wrote:
I'm sure it's here somewhere...
http://www.twinslan.net/~n0nas/manuals/onan/

Yep, This One...
marcsbigfoot20b
Explorer
Mar 25, 2018
You should not run the gen with the generator panel open for more than a few minutes. Air cooling won’t work correctly.
Kpackpackkelley
Explorer II
Mar 25, 2018
Air pulls through the front access louvers left side and out the muffler opening.
TexasUltra
Explorer
Mar 24, 2018
UPDATE…
I pulled it out of storage far enough to add Sea Foam to the fuel tank and change the gas cap. Checked the air filter and it’s still clean. I used my leaf blower to remove anything that might be blocking airflow. I didn’t see much come out.
Started right up…ran for 20 minutes with load and shut down. Nothing blinking on the trouble code, but the compartment did feel hotter than normal when I opened the compartment door.
I set up a fan to blow directly into the compartment with the trailer access door open and the GenSet cover still in place like the instructions state. Started GenSet ran with load for over an hour and a half with no problem. The compartment was much cooler than with the access door closed.
It’s (maybe) a heat issue so I’m going to try and find out how the air flows through the GenSet.
bounder39zman
Explorer II
Mar 19, 2018
since unit will start and run for a period...would indicate that you don't have a "hard" failure... There is not a low oil level switch on this unit. Agree with OP...most likely a fuel delivery problem, and if you pull fault code it will probably be a "36". The fuel pump is likely getting hot and stops delivering fuel, but also have seen control board circuit that powers fuel pump quit working when board gets hot, and this will require a board replacement. Diagnosis requires connecting a voltmeter or test lamp to the fuel pump circuit, then running to duplicate problem, then see if voltage to fuel pump goes away (bad board), or fuel pump just quits supplying pressure. If you pull fault code and is not a "36", then other tests need to be done, depending on code. Probably see this 100+ times a year at our generator shop.
bighatnohorse
Explorer II
Mar 18, 2018
I had the same problem. Putting fuel in the tank fixed it.