We're getting ready for a 6 week trip and found our Onan 5500 generator won't run with a load. We have replaced the carburetor (service code 14) thinking that there might be a speck of dirt causing the problem. The new carb didn't solve our problem.The generator runs fine with no load. If we turn on the air conditioner it runs 4 minutes and shuts off. Always 4 minutes. If we run the microwave it runs, doesn't shut off, but not evenly, not a steady hum. The microwave obviously isn't getting enough power. I'm capable of doing some basic mechanical service. All the RV service places are booked until September and we're leaving soon, with or without a reliable generator. Any ideas would be appreciated!

It is usually a fuel filter or fuel pump issue

The fuel pump has been replaced since we've had the coach but that's not to say it might have failed again. It's getting fuel because it's running. I've just replaced the filter during this issue.

I,D look at the hoses, if there real old one could be colapsing, and it could be your AC going bad pulling more amps than the genset can handle.take a amp reading on the ac when runing.

Sounds like it could be a fuel supply issue. Does it surge a little when you switch on a load? It should, and then recover. If not, then your governor may not be working adequately enough to compensate for the load and the engine shuts down from not getting enough fuel to keep running under load. It could also be the fuel pump...nothing says a new fuel pump can't go bad or a new fuel filter can't get stopped up. Gasoline these days is horrible.I assume that the oil level is adequate? If not, then then the low oil pressure could be cutting it off. Also, some gensets will shut down if they are not producing power. You may want to clean your brushes and the slip ring to make sure there's good contact between the two. You can use a can of contact cleaner or brake cleaner and while the genset is running, spray it on the slip ring. There should be enough friction between the brushes and the slip ring to clean off any built-up carbon or other contaminants. Of course, depending on usage, the brushes may be worn to a point that they are losing contact too.Just a few more suggestions.

Onan Generator Trouble - Won't Run With Load | Good Sam Community

DANO2014
Explorer
Aug 05, 2015
I had the same problems with mine, runs great but with a load it would run a while and shut down. Changed fuel filter, checked all fluids levels but still continue to run sluggish or kill.
Just for your info, I found the problem...there was another inline filter behind the generator that was plugged up plus found some cracked hoses connected to it. Removed inline filter and ran a straight hose to generator and let the fuel filter on the generator do its job. No problems after that....so you might check for another filter or cracked hose...may be getting air?
Just saying, hope you luck.....
GMandJM
Explorer
Aug 04, 2015
Always nice to have a multimeter. Glad you it fixed.

Now you can stay cool.
oldcarfun
Explorer
Aug 04, 2015
All Ok now! Ventura Cummins Service is GREAT! They adjusted the tension on the spring of the carburetor to bring it up to 60 Hz (it was 59) and increased the idle. It's holding the air conditioner now. I couldn't adjust it without knowing what the reading should be and my son's gauges were at work.

They also correctly diagnosed our dash air conditioning problem. It was a small fix and we were on our way home by 2:00.

Thanks for everyone's input.
Gjac
Explorer III
Aug 03, 2015
Another thing I would check for is spark as soon as the genset shuts off. Sometimes the coil stops working when the coil gets hot(a sign that you coil is failing). Is the genset surging under constant load? I just change the control board on mine and found that it had three pots for adjustments. One was to shut the genset down if RPMs get too high. Another thing that can cause the engine to shut down is a loss of signal from the magnetic pick up. Sometimes metal fillings can sick to the pick up head and need to be cleaned off.
GMandJM
Explorer
Aug 03, 2015
Thank you. Lots of Onan questions and issues around here lately.
oldcarfun
Explorer
Aug 03, 2015
We have Cummins field service scheded for Thursday morning in Reno. But.....we tried to leave home yesterday and our dash air would not work. We turned around and came home. Today we are sitting at Cummins Service in Ventura for service on our dash air conditioning. We asked them to look at our Onan generator. I'll report back.
GMandJM
Explorer
Aug 03, 2015
Any update? Just curious.
oldcarfun
Explorer
Jul 29, 2015
We have scheduled service from Cummins in Reno. I will report back. Thanks again.
Busskipper
Explorer
Jul 29, 2015
oldcarfun wrote:
Thanks, all good ideas. Lots of videos on youtube about sliprings, who knew? Our first stop on our trip is Reno (Hot August Nights) and we're told there is an Onan shop close to our campground if we don't get it going. I'll let you know

Not knowing anything about the slipring sounds like a collapsed fuel line, When you get to your first (or you could call ahead to get the number of the local mobile repairman, and have him meet you) - he will likely just work his way back to the problem. If it shuts off it's from lack of fuel or spark. the reason it will fuel back up is because the fuel pump pressure refills the bowl. Only other simple fix would be a pinhole or a fuel filter gasket leak.

Runs but not under load is usually FUEL.

Reportback if you solve the problem,

BOL,

PS - Water?
msturtz
Explorer
Jul 29, 2015
Any cummins shop can work on that generator and many are open evenings and weekends.

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Onan Generator Trouble - Won't Run With Load

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