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Onan 5500 gen help


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I have a onan 5500 gen In my toyhualer.

It runs for about 30 min and dies. If we turn on the AC it lasts about 5 min.

If you try to restart you can't here the fuel pump running to prime it.

I took off the fuel cap and no vapor lock. I opened the float bowl drain and it's dry. If you let it cool down then the pump starts working again.

First thought pump is bad and that's what I'm going to replace but looking at other threads this hasn't solved the problem. No one has figured it out ????

Any ideas?

1) 650 hours on gen

2) oil was low but have topped off

3)fuel was about a month old and bowl is drained after each trip


Thanks for the help guys Charlie

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More than likely it's the fuel pump. To be sure you can send 12V directly to the pump and if it doesn't run you've identified the problem.

Not a bad idea I'll try that.

There is a solenoid on the float bowl that works as a float and tells the pump when to turn on and off. Hopefully it's not that. You can't buy it with out buying the carb.

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Questions: Is the unit mounted in an enclosed compartment? What was outside temperature?


We had an Onan 4000 generator on loan to us from a person that worked for them, but it was mounted in a toyhauler generator compartment with only a small grate style opening on the door for airflow. Usually only used it while travelbg in winter months and didn't have any issues. Started using it more during the summer more and had similar issues. It would run longer if we put a fan on it and left door open. Determined that it was shutting down due to overheating. We did not want to ruin the loaner generator and could not modify the compartment to get more airflow so we gave it back.


Now we have a noisy portable unit that can be moved outside the compartment. Sure do miss the quietness of the Onan.

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Yes it dose have a fuel filter and it's ok.


Round topper

I hope it's not the circuit board that could get spendy


Star dreamer

When problem first started it was around 105' outside and tryed yesterday and it was about 80' I have ran it none stop for days in 120' weather before.


I'm sure it's running out of fuel just don't no why?

And yes it's a lot hotter than normal but I think it's because the motor is running lean when it runs out of fuel.

Thanks Charlie

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Broncohauler, there usually is two filters. One near the fuel pump and another that screws into the carb. The one that goes into the carb could have been replaced by this part number AO26E299 or AO29523. These were bought out by Onan to replace the leaky filters by the carb. Also AirTex makes the fuel pump replacement for less than 1/2 of Onan. http://www.amazon.com/Airtex-E11015-Electric-Fuel-Generator/dp/B0076D5OI2

An Onan is like an old lady, needs a lot of TLC. JMO!

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I recently went through similar symptoms with my 5500. When it would quit, I attempted to start it from the genset panel. When I pressed on the prime/stop button, the fuel hose would vibrate indicating the pump was working at that point. I also disconnected the fuel line from the carb fuel filter and prime pumped about a quart of fuel into a jar looking for contamination. There was none to speak of but the genset still wouldn't stay running. If I sprayed carb cleaner into the carb I could get it to run as long as I kept spraying. So now I was getting the idea it may be the carb was gummed up somewhere. Next, being lazy, I decided to try another cheap trick. So I pulled the fuel line again at the carb filter, emptied as much fuel as I could into my jar then filled the hose with carb cleaner, reconnected the fuel line and bumped the prime pump enought to push the carb cleaner into the carb.

I let it soak for a while, reprimed the carb until the light was on for 10 secs or so, and it fired right up!

End of the problem.

I did add a small bottle of injector cleaner to the fuel tank for good luck. It even sounds smoother now. And, it handles both A/C's without hunting.

This may not solve your problem but it's an easy, cheap trouble shooting/elimination test. You can even sit in a chair in the shade of the RV nose. :o)))

Good luck, I hope this works.


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BH...I went back and reread your post...after reading many of the responses here. For some reason, I didn't see/read what you said about the unit running for awhile. Please disregard my recommendation as its completely off base. My bad.

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I don't think your that far off base. When this happens the fuel pump stops working and the generator runs out of fuel. I can't here it working until I let it cool down.

So I'm still thinking it's the fuel pump ( but it should work or not work) or it's maybe the solenoid on the float bowl.

Doing a google search a lot of people have had the same problem just haven't herd the answer.

Thanks guys for the help so far.

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There have been several posts on other forums, though most describe it not starting at all, other than with carb or brake cleaner.


In all those posts it seems to go down to a switch that is part of the fuel float. The general thought is that the switch gets gummed up from old fuel and then does not engage the fuel pump.


Part of the problem is that Onan does not sell an overhaul kit for the carb. That being the case, you need to be careful if you tear into the carb.


Several folks have described finding ways to get carb cleaner into the float chamber, as mentioned in a prior post, and clearing it that way.


SeaFoam has been mentioned a lot as working well.

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I had the same thing on my generator a few years ago. First replaced filters, then replaced pump. Neither helped. Finally replaced the carb. No problem since. Talking to an old Onan tech he told me outright that all the carb cleaner in the world wouldn't clean these carbs once they get some crud in em. Recently it started acting up again but it seems to be related more to the fuel (ethanol blend) that I put in there, or so I'm hoping.

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I had a issue with my 5500 onan, it would stall occasionally last year and then this spring it would not start at all unless I hit it with starting fluid and then hold the choke shut but it would die as soon as I released it. when I pulled the bowl off I found a bunch of gritty material almost like sand packed in the main jet. one other thing it would not drain any fuel from the drain screw so my initial thought was that the pump was bad, not the case though. after a good cleaning she runs like a champ again.

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