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Old 11-25-2022, 03:01 AM   #1
CRA
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Default ONAN 2500 Propane Generator Won't Start

My 2015 RoadTrek Agile has a ONAN Cummings 2500 Watt propane generator with 34 hours. Usually it starts right up and runs. In October I want to start it and it would crank and crank and crank but not start. LP gas goes to the heater, stove, and water heater and you can smell gas LP gas after it's been cranking so I'm pretty sure that propane is getting to the generator. Changed the spark plug and before I reinstalled, I grounded it and cranked to verify I had spark. It still wouldn't start. My last option I turned on the vehicle and then went back to start it and it started right up. I tried it once or twice the next few days while I was traveling, and it started. Now six weeks later it's doing the same thing cranking crank crank crank but no start with LP odor at the back of the coach outside. I replaced 2 6v AGM 8AGC2 190 ah @20hr house batteries wired in series two years ago and we'll do a battery check them tomorrow. I have checked the Cummings Manual and that says that we need 12v 360 CCA (cold cranking amps) to start the generator. I spoke to a repair center who suggested checking the batteries. I just want to know if anybody has any ideas or if anybody has that similar experience and what you did to resolve it. I'm at my wits end and don't want to take it into the Cummings repair facility if it's not the generator problem. And I don't want to pay $700 for two new batteries. Any help will be greatly appreciated.
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Old 11-25-2022, 01:38 PM   #2
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Unless the generator has been started recently, I Always start the van's engine first - 14+ volts from the alternator.
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Old 11-25-2022, 02:56 PM   #3
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That worked the first time 6 weeks ago and I was hopeful it would be the same. It wasn't. Today I am going to try putting a capacitor battery jumper onthe house batteries which is strong enough for my diesel and an hopeful that will boost enough amps to start the generator. Then I can be certain it is the house batteries. Thanks for your reply.
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Old 11-25-2022, 03:09 PM   #4
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I think the propane generators have had issues with plugged vent lines so that may be something worth checking before going much further.
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Old 11-25-2022, 03:46 PM   #5
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Any idea of the vent line location or what to look for?
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Old Yesterday, 05:51 PM   #6
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A couple of years ago the Onan on my 2016 Roadtrek would not start. I was able to determine that the internal hoses that feed propane to the carburator developed cracks causing the engine to draw air through the cracks rather than pulling in propane. I replaced the hoses (2 of them) and the generator has been fine since. I have since seen articles that others have had the same problem. It may not be what you are experienecing but it is one possibility.
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Old Yesterday, 05:59 PM   #7
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There is a breather line on the generator at the back that should have a sock/screen on it. The sock falls off and insects build nests and block the air. Happened to me with a dirt dabber nest. Once I cleared the blockage, mine then worked fine.
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Old Yesterday, 06:34 PM   #8
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Only 34 hours on a 2016 shows it has not been used enough. Onans need to be "exercised" monthly under load *after* they've been warmed up. Onan recommends 1 hour under load every month. There are "slip rings" in the generator side that get tarnished from lack of use and won't let it start. Servicing those requires the entire unit to be removed to be fixed, not fun *or* cheap.
1st thing to check is the breather vent as described above. It's a hose on the outside back of the green tub it sits in. Wasps and spiders especially like the smell and build nests that plug the hose.
Next thing to check is the oil level. If there's not enough it won't allow it to start to prevent damage.
There is also a fuse and a breaker switch on the unit, make sure it's good/reset.
If you get it started again be sure to run it for a long time under load.
Good luck!
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Old Yesterday, 07:04 PM   #9
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I have a 2012 Pleasure Way Plateau with the 2500 lp generator. Several years (2016) ago my generator was acting exactly like yours and I pretty much did everything you did ( including finding that it would start if the van running). When I replaced my house battery all my problems vanished.

Between the time the problem appeared and when I replaced the house battery I started the van engine anytime the generator wouldn't start. I would not have replaced $700 worth of batteries to fix.

I think the generator just doesn't like it if the battery voltage is a little low.
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Old Yesterday, 07:14 PM   #10
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The fact that you smell propane does not guarantee the propane is getting to the engine. When my unit would not start because of the cracks in the propane hoses, I would smell propane when trying to start it. The propane was being pushed out through the cracks in the hoses. I was abe to verify that it was a fuel issue by partially blocking the air intake to the carburator (essentially choking it) while attempting to start it. The unit would fire and run for a short time as long as the air intake was choked.

As for maintenance, my manual says to run the generator under load for at least half hour every month. In the warmer weather I use the air conditioner as a load; in the colder times I use a small electric space heater as a load.
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