Onan 4000 Starting Issue

[Endlesssummer]

I had planned today to run the generator for its monthly maintenance.
For the first time since I have owned the MH it would crank over but not start. I checked to make sure it is getting gas and checked the spark plug and they were good. I removed the air filter and sprayed some starter fluid and started up and ran like normal. I shut it down and tried to restart and it would not start like before. Again I sprayed starter fluid and it fired right up and ran like normal. Looking for some direction on what the next step might be.
Thanks

 

[DonTom]

I had planned today to run the generator for its monthly maintenance.
For the first time since I have owned the MH it would crank over but not start. I checked to make sure it is getting gas and checked the spark plug and they were good. I removed the air filter and sprayed some starter fluid and started up and ran like normal. I shut it down and tried to restart and it would not start like before. Again I sprayed starter fluid and it fired right up and ran like normal. Looking for some direction on what the next step might be.
Thanks

Even though you say you have gas, it could be just residual. How full is the RV gas tank? Be sure you're above a half tank, especially if not level. If level, above a third tank. But I like to have a full RV gas tank when I am testing anything on my Onan. They are designed to not run when your RV gas tank is low. But they will still crank fine.

If that has nothing to do with it, is your genny showing any error codes? What is the year RV and check the model number in the genny (look for it on the genny plate itself). There are many models of an Onan 4000 and there are differences between them.

-Don- Auburn, CA

 

[Endlesssummer]

I was aware of the low gas situation so I did take the MH out and filled it up hoping that was the issue and it was not.
The generator- RV QG 4000 model # 4KY-6747 R.

 

[Endlesssummer]

I forgot to add that there are no codes coming up.

 

[Henry J Fate]

If it fires up with starter fluid and then runs normally, the choke assembly is first on the list.

The choke increases fuel to the air mixture for starts. The colder the temperature at start up, more dependency is placed on the choke assembly. Warmer temps will not require much choke if any.

Generally, it is still possible to start the engine without a choke. The starter fluid is one way. Another way is excessive cranking which will eventually put enough fuel into the engine.

Once the engine begins to run, the choke is not needed as the combustion chamber begins to heat up. The choke assembly should be fully closed at start up. It will then fully open when running.

 

[Endlesssummer]

When the gen is running started by starting fluid and ran till warmed up shouldn’t the choke not be a factor. When I try to restart right after shutting it down it will not start.

 

[Henry J Fate]

I believe that to be correct.


Maybe there is a fuel blockage that is overpowered when the genset fires up with the starter fluid but is not overpowered when its turned over by the battery and starter only.

Probably time to clean everything and give it a full service.

 

[Henry J Fate]

I do not know of any electronics or controls that would cause such an event. There is a fuel cutoff but i do not think that could cause this event.

When you say it will not start after being warmed up, does it give any indication of fuel burning or does it just spin like its got no spark ?

 

[DonTom]

. I removed the air filter and sprayed some starter fluid and started up and ran like normal.

Perhaps very low fuel psi? Clogged gas filter or very weak fuel pump perhaps?

And as crazy as this could sound if you're using a Champion spark plug, I would change it. They do weird things in the Onan 4Ks

-Don- Auburn, CA

 

[Endlesssummer]

I did remove the gas line going to the carburetor and then cranked the generator and there was a strong steam of gas coming out. So it might be the carburetor is acting up.

 

[DonTom]

I did remove the gas line going to the carburetor and then cranked the generator and there was a strong steam of gas coming out. So it might be the carburetor is acting up.

As Henry mentioned, I would check to make sure the choke is okay, not stuck closed. Check the linkage that all seems okay.

Does it start every time with no hesitation with the starter fluid?

Seems like an unusual problem. But I once had a pin break in my carb while it was running and I replaced the carb with a cheap $40.00 one from Amazon that worked perfectly.

BTW, that was the very first time I had any genny problem, so I didn't even know where to start. But I got all the help I needed from Isaac-1 and others in this forum.

-Don- Auburn, CA

 

[udidwht]

How did you manage to get to operating temp with starter fluid alone. That is not recommended.

 

[Endlesssummer]

Just getting back to report results.
To answer the last reply I just wanted to see if it would start with the fluid which it did and ran on its own for as long as I would allow, but was surging up and down.
As a last resort, I mix 4oz of sea foam in one gallon of 91 octane. I disconnected the gas hose going to the gas tank and put it in the one gallon container. I started with fluid and let it run for 30 min. Shut it down and it restarted without fluid. Ran for another 30 min and shut down and reconnected the gas hose. It now starts at the control panel like it should. Tested it under load and ran very well.