Onan 4K generator quits after 8-15 minutes of run time.

CambriaRista · 08-29-2018, 01:40 PM

Dealer’s tech suspects overheating but can’t come up with a solution - Onan doesn’t provide phone tech support.
Oil is good & only 97 hours on a 2008 coach. Space around generator is clear of debris.
Appreciate any ideas.

powercat_ras · 08-29-2018, 02:05 PM

If it is happening when its hot outside and not windy then overheating is most likely. Try running it with the side of the RV generator access door on the RV wall open (not the access door right on the Onan). If it runs longer with the RV wall side access then its likely just overheating due to the generator air cooling hot air exhaust that exits the bottom of the generator rising back up and getting into the generator intake so that the generator is sucking in much hotter air than ambient temp air.

Ranger Smith · 08-29-2018, 02:07 PM

Number 1 cause of your symptom is the fuel pump.

CambriaRista · 08-29-2018, 02:14 PM

Thanks!
It was in the shop bay with coach access door open and a fan blowing on it according to the tech. Got more minutes but not more than 15. Some suggested an oil cooler or oil temp sensor issue. Without a temp gauge it’s hard to tell what’s real; false sensor indication or really overheating?

powercat_ras · 08-29-2018, 02:46 PM

Hopefully he had the Onan side cover on when he did his shop test. The way the 4000 is made the side cover MUST be on or the air cooling will not blow air across the engine and generator.

If you read your Onan manual it tells you how to use the Generator's manual start button to show the fault code it saved the last time it stored a code. It is read by counting flashes on the light in the start button. Did the tech read the code after it shut down and tell you the code was overheat shutdown or is he just making his own educated guess?

If it was me working on it I would do all the easy Onan things first - - - Change air filter, change oil, make sure altitude is set correctly.

CambriaRista · 08-29-2018, 03:28 PM

Not sure if the Onan door was closed - my guess it was open - I wasn’t there. He did mention not seeing a code but he was looking at a square red window (could be the start button?) he didn’t mention counting flashes. Air filter is clean as is oil. Not sure about altitude but might be something to check; I assume manual explains how it’s done. I’ll try your suggestions B4 spending on a mechanic.
Thanks!

lotsoftoys · 08-30-2018, 06:46 AM

Cummins does offer a tech support line. 1-800-CUMMINS.

wmckinley · 08-30-2018, 06:57 AM

X2 on Ranger Smith. Had same symptoms on mine 5.5kw. Replaced fuel pump, no problems since.

CambriaRista · 08-30-2018, 09:36 PM

Thanks,
Is there a way to test the pump? I did get a Fsult code today - 36 - per manual chk fuel line (pump?) air filter and spark plug. Might try the easy & cheap solutions first.
If it’s the fuel pump would it even run 8 minutes?

wmckinley · 08-31-2018, 07:44 AM

CambriaRista, My system had the same symptoms. It would run anywhere from 10 to 22 minutes. When I replaced the fuel pump i also replaced the fuel filter. Replaced fuel pump first, tested generator, ran for 2 hours with load. Then replaced fuel filter. Has run great since. I had done plug and air filter previously. I do my oil and filter every 50 hours, more often than required, replace air filter as needed.

CambriaRista · 09-01-2018, 12:34 PM

Thanks!
So three examples of symptoms similar to mine all pointing to the fuel pump. Coach is a 2008 and Onan has 97 hours. Wouldn’t have thought of the fuel pump especially since dealer was pretty sure it’s an overheating problem.
I’ll try inspecting/replacing the plug. If persists I’ll invest in a new fuel pump.
Thanks for the feedback - I’ll post results.

jl12345 · 09-01-2018, 03:53 PM

Have the same problem. For our diesel generator Winnebago incorrectly installed the return fuel line and tied it into the vehicle fuel return line resulting in back pressure of>10 pis and generator to shut down. Cummins cannot fix. This is a design flaw in the Installation by Winnebago. No solution other than to run line from generator to diesel fuel tank but this would void the Sprinter warranty and potentially cause a safety issue.

CambriaRista · 09-04-2018, 09:28 PM

Thanks,
Hopefully my gas model’s fix is easier and based on feedback seems fuel pump is the culprit - but I musn’ assume.
Good luck with your diesel gen!

**creativepart** · 09-05-2018, 09:13 AM

In a way you're lucky. Your dealer can reproduce the problem. Our 4000 routinely shut down after an hour or so and on restart wouldn't run 5 mins. It did it EVERY time we ran it. Took it to a Cummins dealership. They ran it 8 hours a day for 3 days - actually used 3/4 of a tank of gas. It never once quit on them. So, no fix.

We sold that coach - so I guess it's someone else's problem now.

CambriaRista · 09-05-2018, 09:27 AM

Thanks for sharing - boy, must have been frustrating! It's like "it hurts, but not when I'm at the doctor's..."
Good luck with the new coach!

Teamfoxy · 09-06-2018, 07:14 AM

I will make it X4 on the fuel pump likely being the problem. My understanding, from what others say, is that the rubber parts expand and stop the pump until they cool down. The problem is worse in hot weather which of course leads one to think it might be a vapor lock or the oil sensor shutting down the generator.

After the generator shuts down, immediately disconnect the hose from the carburetor and press the prime button. If no fuel is coming out, that is your answer.

You can buy a new fuel pump and filter on Amazon for less than $80. It is not hard to replace, but you do have to remove the control module to access it. The hardest part was loosening the torx bolt holding down the pump. It was hard to position the driver and have enough leverage to break it free. Fortunately my son had a right angle extension for his impact wrench and that did the trick.

CambriaRista · 09-07-2018, 06:15 AM

Thanks! Good suggestion for testing fuel flow.; I’ll do that to confirm pump is indeed the issue. Symptoms seem to match a fuel flow problem as the gen doesn’t shut down abruptly as if turned off by a overheating switch rather it starts to hesitate for several seconds then quits. Still seems strange that it would restart right away though. I’ll definitely give this a try.

Teamfoxy · 09-07-2018, 07:32 AM

Quote:

Originally Posted by CambriaRista

Thanks! Good suggestion for testing fuel flow.; I’ll do that to confirm pump is indeed the issue. Symptoms seem to match a fuel flow problem as the gen doesn’t shut down abruptly as if turned off by a overheating switch rather it starts to hesitate for several seconds then quits. Still seems strange that it would restart right away though. I’ll definitely give this a try.

I did not catch the short restarting time. 97 hours on a 2008 unit probably means a lot of time sitting which is not good for the fuel system. Also, the sensor cuts fuel flow, so would sound exactly like you describe. So before going further, I would pull the carburetor bowl and the sensor on the bottom and clean them and check for corrosion. Soak both in SeaFoam for an hour or so, clean as much as you can and then run the SeaFoam treatment from a separate fuel source per their instructions on You-Tube.

My son and I did that prior to replacing the fuel pump because the generator was running rough, starting hard, and quitting. Cleaning the carburetor and running the SeaFoam treatment got us running well, but it was still quitting after 45 minutes and would not restart until it had cooled off. After the generator stopped, the fuel pump still clicked, but there was no flow of fuel. After sitting, the fuel flow was fine.

I've put 96 hours on our generator this summer after reworking the fuel system and it has run great. We have 835 total hours on it.

CambriaRista · 09-11-2018, 12:28 PM

Again, thanks for the tips. I’m @ the RV now & wondering how the heck to remove torx screws with so little room for a driver - I don’t have an angled tool. So checking for ideas again I read your latest post - carburetor is a good place to start for sure! But I did try the fuel pump test: started right up & ran smoothly for 8 minutes then started 30 seconds of hesitation till it finally quit. Tried restarting immediately without success but did start after a 6 minute cool down, only running for 2 minutes. I disconnected the fuel line & pressed prime button - nothing. Then pushed starter and got a slight trickle at first then nothing. So now I have to decide whether I want to invest in the tools & time to change the pump... will add carb cleaning to the “to do” list as well
Thanks again!

Teamfoxy · 09-11-2018, 01:41 PM

The link below will show you the tool my son had and used. I bought one for $18 on sale at Ace Hardware. https://www.zoro.com/dewalt-right-an...review-display

The torx driver bit attachment would be another $2-$3 but I already had a set of those.
You need to remove the starter solenoid and the control board to get at the fuel pump. They have the same size torx screws holding them in place. Have a pencil or something to stick in the fuel hose when you take it off. There are several videos on You Tube that will show you how to do it.

I looked up what I paid for the fuel pump and filter. It was $67 on Amazon including the shipping. Worth buying a couple of tools because labor at the local RV shop is $110/hr plus they will charge you retail for the parts. Also chances are they will not get to you for at least several weeks.

At this point, I don't even think about taking the RV to a shop. There is a You Tube video on how to fix just about anything and you can have any part you need delivered anywhere you are in two days. Easier, faster, and a lot less frustrating to do things yourself