ONAN runs, stops, starts again

[TexasUltra]

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: 4KYFA26100K
SER: H050816555
SPEC: K

[TexasUltra]

Thanks, everyone for the help, advice and a little humor thrown in. It was the fuel pump ($59)

[Sam_Spade]

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]

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]

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]

TexasUltra wrote:
I'm sure it's here somewhere...
http://www.twinslan.net/~n0nas/manuals/onan/

Yep, This One...

[marcsbigfoot20b]

You should not run the gen with the generator panel open for more than a few minutes. Air cooling won’t work correctly.

[Kpackpackkelley]

Air pulls through the front access louvers left side and out the muffler opening.

[TexasUltra]

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]

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]

I had the same problem. Putting fuel in the tank fixed it.

[TexasUltra]

I'm sure it's here somewhere...
http://www.twinslan.net/~n0nas/manuals/onan/

[j-d]

First, Congratulations and Thanks for posting Model, Serial, Spec information! We have 4KY Spec K also. If fuel pump had been replaced by previous owner, don't know. Carb HAD been and was already fouled with gum when we bought the coach. Luckily an OP here had a good used one he was willing to part with...
I met a fisherman/camper I'll call Old Joe. He was running his 4KY and it just hummed. Mine (before carb replacement) would start, and it would run as long as there was load on it. Once hot, and once load dropped off, it would stall and I could not re-start it. Old Joe told me "Every drop of gas that goes into my tank (which was the 55-gallon tank on a Ford E450 under a Class C) gets Stabilizer in it." I said "Even on long trips where you're only filling up for the road?" and Old Joe said "YES!" Since the new carb, I've added stabilizer every fill-up. I also try to exercise the 4KY regularly. But since I'm an irregular kinda guy, sometimes it's less often than monthly. Nonetheless, simply faultless genset operation.

Since you buy good fuel, add stabilizer and exercise the genset I'm going with the Fuel Pump crowd on this one. The ONAN Service Manual you'll probably find is 981-0530C. The 0530 without "C" is for older 4KY's. Others here can probably post a download link. I haven't had any luck finding one today, but if you PM me with your email ID, I can send you a copy as attachment.

0530C will give you Codes, Troubleshooting Chart, and Fuel Pump Pressure spec. Code'll probably be "36" which kinda means "Beats Me" and I'm concerned that by the time you connect a fuel pressure gauge, a bad fuel pump could have cooled enough to look good again.

Let me add this: Many Marinas pump ValvTect marine gasoline. It's stabilized, disperses moisure, cleans injectors, on and on. I am a Reformed Skeptic about ValvTect! Honda engine on my Pressure Washer needed carb cleaning every few months if I forgot to run it when I used automotive regular. Adding StaBil did a decent job but the fuel lines on the String Trimmer still kept failing since it was Ethanol gas. The ValvTect available in Florida is both Unleaded and ETHANOL FREE. I believe Octane is 89. I just bought my start-of-mowing-season supply. Paid $4 a gallon while plain old car gas is $2.50. Worth every dollar, every drop. If you can get to ValvTect, by all means DO!

[Gottahaveit]

Recently had the same problem...replaced fuel pump and works like a charm

[TexasUltra]

All good advice and things to check. Vapor lock was one of the things I'd thought about but not some of these others. Thanks, I'll update soon.