Onan 4000 shutting off after 20 min.

These posts contain Onan, shut and heat.

I have had my 4BGE Spec G do this twice.

First thing I would recommend is you get yourself an inline spark tester like this:

https://www.amazon.com/gp/product/B0002STS4O

When the generator refuses to start/run, put this inline with the outboard spark plug and see if you are getting a spark. I bet you are not.

There are two primary suspects - the coil and the ignition control module (assuming you have electronic and not points ignition).

You can get aftermarket coils on Amazon for about $35. Ignition control modules run $100+.

I sent my voltage regulator and control board off to Flight Systems, who will test them for $35 each. If you end up buying a replacement part from them, they waive the testing fee. Both boards are ~$200 each.

It's also possible that the fuel pump is dying.

For me, it was either the ignition control module or the coil. I can't be sure which because when I was replacing the ICM the terminal on the coil twisted out of the coil so I had to replace it also. So I can't know which was the culprit, but it was one or the other. I'm pretty sure it was the ICM though.

Steve

I think by far the most common cause of this on these generators is the fuel pump dying such that it doesn't work properly when hot. You may be able to verify that by comparing the sound it makes in priming mode (holding the control switch in the off position when the generator isn't running) when it's cold vs. when it's hot and has just died. Most, but not quite all, versions of the 4KY have the prime function.

While ignition system components can also get temperature sensitive, and that's not unheard of, it's not anywhere near as common as the fuel pump, from what I've been able to suss out.

DrewE wrote:
I think by far the most common cause of this on these generators is the fuel pump dying such that it doesn't work properly when hot. You may be able to verify that by comparing the sound it makes in priming mode (holding the control switch in the off position when the generator isn't running) when it's cold vs. when it's hot and has just died. Most, but not quite all, versions of the 4KY have the prime function.

While ignition system components can also get temperature sensitive, and that's not unheard of, it's not anywhere near as common as the fuel pump, from what I've been able to suss out.

Yea I have the prime function. I ran it yesterday and it shut down 4 times. To trouble shoot the fuel pump I tried to start it as soon as it stopped and got it running right away every time but had to prime it. I ran it with no load and ran it with the AC on, same result. That leads me to believe it's not the pump because it would run with no cool down. The weird thing is after the 4th start it ran for 2 hrs until I shut it off because I had to leave. Came back and hour later started it and ran for hours until I finally shut it off. I know my way around an engine just not that familiar with all the different components of an Onan. I can't trouble shoot now if it won't shut down. Going to start it now and then to see what result I get.

Sounds like a vapor lock situation. Check the routing of your fuel line on the suction side of the fuel pump to make sure it is away from heat sources. Also check it for possible cracking where the pump could be sucking in air.

I had this exact problem with my onan 4ky..... I could predict exactly how long it would run.....


It was my magneto that was heating up and going open....

Yea I have the prime function. I ran it yesterday and it shut down 4 times. To trouble shoot the fuel pump I tried to start it as soon as it stopped and got it running right away every time but had to prime it. I ran it with no load and ran it with the AC on, same result. That leads me to believe it's not the pump because it would run with no cool down. The weird thing is after the 4th start it ran for 2 hrs until I shut it off because I had to leave. Came back and hour later started it and ran for hours until I finally shut it off. I know my way around an engine just not that familiar with all the different components of an Onan. I can't trouble shoot now if it won't shut down. Going to start it now and then to see what result I get.

Sounds just like mine that I just got fixed. One time on a trip last may it ran overnight no problem, but every night after that it ran for less and less time.

You can replace the coil fora bout $35.
You can replace the Ignition Control Module for about $100.
You can replace the starter for about $35.
An inline spark tester is about $10.

If you find you are getting no spark when it shuts down, I would probably just replace the coil and ICM from the get-go. It's possible it's the voltage regulator ($250) or the control board ($200) but Flight Systems will test those for you at $35 a piece and the testing fee is waved if you buy a replacement from them.

But if I got no spark and had to do it over again, I'd just drop $150 and replace both the coil and ICM from the get-go. They are easy to replace. You have to crank the engine to the right spot so that the short cooling fin lines up with the ICM or the ICM won't come out of the housing. That's the only trick.

Make sure you polish your slip rings - resistance at the brushes should be around 20 ohms and if you get higher than 80 you risk frying the voltage regulator. Flight Systems make a Slip Stick ($20) you can use to reach in and polish the rings or you can do it with a dowel rod and some brown Scotchbright material and use some dental floss to bind the scrubby to the dowel rod and use that.

Steve

Thanks guys. Going to run a few more times this week and see what happens. Last 2 times it didn't shut down and it's hard to trouble shoot when it won't shut down. I doubt it fixed its self.