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Onan JC Stumper


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  #1  
Old 11-26-2016, 09:30:26 AM
captainjdog captainjdog is offline
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Default Onan JC Stumper

Good Day all.

First time question asker here:

Working on an old Onan JC 4 cylinder with propane, and it has me stumped.

History: I've had the generator for about 8 years and never had a problem. Until, last week when I routinely run the generator but the momentary stop button wouldn't shut the engine off. The switch has been problematic in the past. So, I had to shut the propane off to get the engine to stop (First time doing this - usually leave the propane on), I replaced the off switch.

Problem:
Here is where things get weird. The engine will not start with the propane ON. If I turn the propane OFF and give it a squirt of carb cleaner the generator kicks off and runs. If I turn the propane ON...NOTHING! Give it a blast of carb cleaner...Nothing... I checked for spark and I have spark!.

Temporary Solution: So the only wires having anything to do with propane ON/OFF is the propane solenoid. So with propane ON, I disconnected the solenoid and the generator kicks off with some carb cleaner. So I made a jumper to disconnect the solenoid from the generator control and run it directly to the battery. Generator fired right up and runs fine.

Theory: I studied the wiring schematics and it seems the solenoid shares the positive battery with the coil. The solenoid seems to be working correctly. Perhaps it is pulling too many amps when the propane is ON weakening the coil? I checked the voltage the generator control is providing the solenoid and its about 9.8v, battery has a healthy 12.5v.

Questions: Should I have 12v at the solenoid?
Should I replace the propane solenoid?

Any other ideas?

Thanks in advance.
V/R,
Justin
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  #2  
Old 11-26-2016, 09:37:26 AM
JohnnyC JohnnyC is online now
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Default Re: JC Stumper

I am on my way out the door when I was shutting off the PC and read your post. First, welcome... Second, yes - you should have 12 VDC at the solenoid when starting and running the JC. To be clear, I am writing about the solenoid next to the demand regulator.

You will be asked to post the complete model and serial number of your JC to best figure out the issue you are experiencing. There is tons of wiring information here including wiring diagrams.

JohnnyC
New Jersey
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Old 11-26-2016, 11:14:14 AM
captainjdog captainjdog is offline
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Default Re: JC Stumper

Thanks for the response, Yes that's the one.

I've been studying the wiring diagrams, looks like I'll just have to trace the connection to figure out where my voltage drop is. I'll update my findings.

Model 12.5JC-3R/2539R
Serial 17C995911
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Old 11-26-2016, 01:00:39 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: JC Stumper

I would imagine there is no mouse damage in the control box! Was there ever any damage in there when you got the unit? The start relay could be going bad. You might spray down both the start and run relays with contact cleaner.
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Old 11-26-2016, 02:26:22 PM
captainjdog captainjdog is offline
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Default Re: JC Stumper

I took the start relay apart as I had 12.6v going in and only 9.8 coming out when engaging the start button. It was clean though the contacts had a little corrosion, I cleaned it and put it back together and still got 9.8. I'll try to find a replacement. Oddly the generator started and ran.

Unfortunately after about 30 seconds of running with no load, smoke was boiling out of the giant round metal generator vent cap. I shut it down removed the end cap and the black box was smoking. I don't think the two systems are related, as I don't see how messing with the start relay did anything with generator part, but who knows.

One step forward, one step back
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Old 11-26-2016, 02:46:33 PM
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BigBlockChev BigBlockChev is offline
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Default Re: JC Stumper

If your set has a magneciter voltage regulator then running the set at less than 1800 rpm can overheat the coils of the magneciter Some pics of the whole set will tell us whether that is the case.
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Old 11-26-2016, 02:48:04 PM
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Default Re: JC Stumper

Uh.Oh!! magic smoke. I hope ya didn't smoke the magniciter.
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Old 11-26-2016, 04:21:26 PM
captainjdog captainjdog is offline
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Default Re: JC Stumper

The two little round parts were squirting juices and smoking.

I'm not sure what RPM it was running at, It started and ran noticeably lower rpm for 8-10 seconds then the rpm picked up and it smoothed out and sounded really good (normal to me), then about 20 seconds later I noticed the smoke coming out of the side vent.

I was also noticing light smoke during all the previous troubleshooting, but never ran long enough, I figured it was animal or bug stuff. Tried smelling it and wasn't too concerned because it didn't really smell electrical. I was wrong

Hopefully you can see the attachments.
I know its dirty, first time I've taken that cover off.
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Old 11-26-2016, 05:00:30 PM
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Default Re: JC Stumper

Wow that looks like some kind of aftermarket Magneciter replacement!! I have never seen one like that, possibly Billy or one of the other oldtimers has run across that. As far as the starting issue I might suspect that the zero governor is either leaking past resulting in a rich fuel condition or possibly has a hole in the diaphragm and is not opening at all at cranking speed , or just bad points or condensor. Cheers Dan
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Old 11-26-2016, 06:24:17 PM
captainjdog captainjdog is offline
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Default Re: JC Stumper

Yeah, I thought it looked newish too. Its an ONAN part. (See pics)

I haven't tinkered with it anymore today, its cold and windy, and I have a case of the F#$ its.

The zero governor rich condition would make sense with my symptoms, and the roughness at first start up till it leans out. I'll check that out.

I assume I should disconnect this magniciter before any further damage is done, until I can verify RPM? Is there anything else I should be concerned about? The house is completely disconnected until I have faith this thing is working correctly.

Thanks for all your assistance so far everyone, This forum is truly wonderful.
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