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 > Help! Onan 4K generator refuses to start and stay on

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Kennyg

Green bay, Wi 54303

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Posted: 05/15/21 06:49am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

What he said ^.
Gasoline or LP? Presume gasoline.
Does it start and run 15 sec repeatedly or was it one and done?

Blue smoke is oil.
Not necessarily an issue. Could be from sitting, could be burning a little oil but still ok.
A lot of people don’t even notice, but most engines, new or old, in my experience, will blow a little blue smoke on startup. Once in a while. Could be a chunk of carbon holding a valve slightly open, sticky ring that frees itself up or any other number of things.

If it does it every time cold and then clears up, likely worn top end valves etc. if it smokes after warmed up and constantly then likely rings.

Is the crankcase over full ( gas draining into case, stuck float on a gravity fed, primer stuck on and you didn’t notice etc)? If so it could be sucking in diluted oil. Could also make it not run right, maybe.
From there, could be carb plugged up
Need more history and symptoms.
Old gas, sat for a long time?
Original question is it repeatable runs and dies?
If no restart, does it fire on ether?
Is the fuel pump working consistently? Did you check it?


This is a replacement carb only two years old. The oil in crank was replaced at same time as carb. I over filled this jan. removed the excess and noted it was already dark brown. Replaced original sparkplug this january. When starting, it is repeatable start and stops. Pump does work. removed gas line and attempted start; gas flowed out of line when start button is engaged.


Kennyg

bobndot

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Posted: 05/15/21 08:08am Link  |  Quote  |  Print  |  Notify Moderator

When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.

Grit dog

Black Diamond, WA

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Posted: 05/15/21 09:52am Link  |  Quote  |  Print  |  Notify Moderator

bobndot wrote:

When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.


This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?


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Grit dog

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Posted: 05/15/21 09:54am Link  |  Quote  |  Print  |  Notify Moderator

Kennyg
Unless it’s something weird cutting the ignition/spark off, my money is on plugged carb or carb issue.
Did it sit with gas/old gas in it for a while and not run?

Kennyg

Green bay, Wi 54303

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Posted: 05/15/21 01:44pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

Kennyg
Unless it’s something weird cutting the ignition/spark off, my money is on plugged carb or carb issue.
Did it sit with gas/old gas in it for a while and not run?


Yes, approx 6 months.

Kennyg

Green bay, Wi 54303

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Posted: 05/15/21 01:46pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

bobndot wrote:

When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.


This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?


also saw the video and I've since reduced the oil level to the half on the dip stick.

JaxDad

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Posted: 05/15/21 03:56pm Link  |  Quote  |  Print  |  Notify Moderator

Onan 4K are notorious for simple issues causing problems.

The very first check you need to do is start it with the remote but do NOT let go of the “start” button when it starts.

If it continues to run, hold the button for 30 seconds then let go. If it stalls right away again, then get a known good battery or another vehicle and put booster cables on the house battery and repeat the same test again.

If it continues to run with the booster cables the voltage in the house battery is too low. Charge or replace it.

If it doesn’t continue to run, it’s a fuel issue.

bobndot

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Posted: 05/16/21 11:13am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

bobndot wrote:

When u check the Onan 4000 oil level is the oil up to the full mark on the dipstick ? If so it might be over full.
I always pre-measure the amt of new oil that add during an oil change , then note it on the dipstick as my full mark.

There is a video of an Onan faulty dipstick where the full mark should read 1/2 way between full and add lines. As per the video, this has been resulting in your symptoms of starting, blue smoke then stopping.


This is good to know as I’ve never had one before until now and basically couldn’t get it full. Think it’s about half way up the dipstick. How the ___ do you get the dipstick length wrong? What’s the capacity supposed to be?


Dipstick engineering can be tricky business and requires 8 addition years of residency before they let you loose on a real generator. [emoticon]

Onan RV recommends changing the oil every 100 hours or once a year, whichever comes first. It only takes about 20 minutes and you will be good to go for the season. You will need a T30 torx bit, a 12mm socket, an oil pan, a funnel and 1.6 quarts of SAE30 or 15W-40 oil.

Grit dog

Black Diamond, WA

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Posted: 05/17/21 10:05pm Link  |  Quote  |  Print  |  Notify Moderator

^Awesome Thanks!’
That’s good seems about the amount I got in there.

Kennyg. Yeah if the battery deal isn’t the problem. Not likely if you’re using the rig.
Then I’d probably take the carb apart and clean er out.

ron.dittmer

North-East Illinois

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Posted: 05/21/21 05:27am Link  |  Quote  |  Print  |  Notify Moderator

Hi KennyG,

I had a problem last fall with our Onan 4000 generator. It would self-shut down after 20 minutes running. I replaced the fuel pump with fuel filter just yesterday and the generator is perfect again.

The fuel pump was not easy to replace, but can be done. I highly recommend you consider replacing your fuel pump & fuel filter together. I recommend getting one with the exit tube like this (like the original one) to avoid a potential interference problem that I dealt with with the other available design.
[image]

Everyone on these RV forums quickly zero in on the carburetor being the problem, most especially because the unit sat idle for too long and bad gas in the carb gumming it up and such. At risk of insulting others, I don't agree.
I would replace the fuel pump and fuel filter together. It's surely cheap enough. It's all in the labor.

If you decide to do it, first disconnect every battery for the house and chassis. You will need to disconnect lots of wires in the area, remove the solenoid, then the control module. There is a 30 pin connector plugged to the underside of the control module that is very hard to access. I pulled every cable and wire harness out from the work area to gain enough work space.

When disconnecting and removing the fuel pump, make sure to first protect that 30 pin connector with a good rag to absorb any spilt gas.

Repeating what I said many months ago here in this subject, I never run my generator during storage which is typically 7 months but has been as long as 2.5 years, with the gas in the main tank being that old. Starting involves a lot of pump-priming, then chugs a bit and soon smooths out. The main chassis engine starts right up like it ran just the day before.

Carbs for simple engines are a lot more forgiving than people give credit.

* This post was edited 05/21/21 07:25am by ron.dittmer *


2007 Phoenix Cruiser model 2350, with 2006 Jeep Liberty in-tow

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