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Old 08-02-2011, 09:00 AM   #1
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Onan 4000 runs w/switch on only, no output

I've searched online and here on the board, haven't found an answer yet---

Onan 4000, which is in our 1995 32' Party Cruiser (boat)-- I don't know the model but it's basically identical to the 4000 that was in our 1992 Winnebago, it's not a "marine" version, or a newer 'computerized' genny...

Last time I used it was early last year, just to see if it was working, and it worked fine, powered up the AC while I vacuumed out the boat...

Last weekend it fired up after its usual 10 second first-season-start waiting time. Only the light on the remote power switch didn't light up and the power gauge didn't budge. And it stops upon releasing the switch.

Keeping it running with my toe on the switch I found no power output anywhere. The on/off switch on the genny does the same thing. I checked the 5 amp fuse, it was fine. I removed the wire connector on the side, no loose wires or other issues. I flipped the breaker off and on, but I know that doesn't have anything to do with the light on the switch getting power anyway, it's only for the 120vac out...

I did find online this info: The battery powers the ignition until the genny powers up, then it takes over all 12 volt activity. In order for the genny TO power up, 3 things must happen:
It must receive a "start" signal-
It must receive an "ok" signal from the oil pressure switch-
It must NOT receive a "stop" signal...

What I didn't find online is how to troubleshoot, or find the various parts TO troubleshoot...

I'm pretty sure it's not receiving a stop signal, as I know that while stopping the genny with the switch, the switch light remains ON until the genny fully stops...

This leaves either an oil pressure issue, or...?? --I just need to know where to look!

Any advice, diagrams, anything would be great, thanks!

<edit>, found a pic that shows the genny and the model/serial number. (forgive the grime)
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2000 40' Tiffin Allegro Bus \ 2003 Chaparral 260 SSI
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster
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Old 08-02-2011, 02:59 PM   #2
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Take the panel off with your start switch on it and take a look behind it.
You may need to spray a contact cleaner to clean corrosion on back of panel.

98KSCA, 99MACA, 03 KSCA-3740- 8.1 Chev-- ALLISON Trans, now in good hands
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Old 08-03-2011, 09:03 PM   #3
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Here is the service manual for your generator (4.0 BGE Spec K):

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Old 08-03-2011, 09:16 PM   #4
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sounds like the generator is not putting out ac. once you release the switch it must get the juice to keep it running from the gen.
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Old 08-04-2011, 07:47 AM   #5
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It does have oil in it, and the oil doesn't smell like gas, right?
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Old 08-04-2011, 07:52 AM   #6
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Dirty slip rings bad brushes. It has to excite the stator before it will output voltage. Check and see if a critter built a nest in the windings.
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Old 08-04-2011, 08:14 AM   #7
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Onan Generators - SmokStak
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Old 08-05-2011, 12:31 PM   #8
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Many thanks for the responses!

All is fine in the oil/gas department. We haven't used the boat since 2006, but I have run the genny a few times every summer, usually to run the vacuum and the AC while cleaning the thing (as noted above). It's always started up, and always worked fine. This year the only difference is no power output whatsoever.

A critter could definitely be an issue, although there's no other signs of critters except for the cats that live at the harbor (which help with the critters!)

I'll peruse the manual supplied by Dave and the nice Onan info supplied by Midniteoyl (thanks guys!) and hopefully I'll find a cause and cure-- if/when that happens I'll be sure to post the solution!
2000 40' Tiffin Allegro Bus \ 2003 Chaparral 260 SSI
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster
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Old 08-05-2011, 08:39 PM   #9
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As others have noted, the genset will shut down if it is not generating power. Holding the switch down overrides that, as long as battery power is available.

I suspect that moisture has built up in the stator or armature from lack of use. Running it a couple times is not enough - it needs to be run to operating temperature, under a substantial electrical load, every month to prevent moisture from deteriorating the internal wiring. I also suspect it is going to be a very expensive repair.
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Old 08-06-2011, 09:19 AM   #10
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Utah is the 2nd driest state in the country, where we whine when the humidity gets above 40%... our moisture problems usually arise from broken plumbing, or doing things like this--- \ (no, it wasn't me, but I did have the camera ready!)


What we DO have problems with out here (at the harbor especially) is wasps and spiders, if there's a place for wasps to get in, they'll build those mud honeycomb things everywhere. And the spider webs and the bugs caught in them can get real thick. If there is a problem with the internals, I expect bugs to be the cause...
2000 40' Tiffin Allegro Bus \ 2003 Chaparral 260 SSI
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster
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Old 08-06-2011, 09:25 AM   #11
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I just got done spending $675 at Cummins to fix my gen. It seems the slip rings got dirty which blew out the reg. Same thing you have would not keep running. At the dealership while paying $490 for a new reg I looked the number up on Ebay and found one new for $45..... So now I'm going to buy a spare reg. and fuel pump for next time....
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Old 08-07-2011, 07:09 PM   #12
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Well, I got off easy--

Seems 007 nailed it...

I hand drew up some of the diagrams from the manual, grabbed some tools and a voltmeter and headed for the boat to do some tests. I got as far as removing the switch cover, and noticed the switch and the female side of the wire connector was all part of a one-piece 'unit'. Not sure where to look next, I blew some dust off the wires, and for kicks I pressed the start button. She fired, but this time she stayed running when I released the button!

I still had no power to the remote switch--- ah, ok, plug the connector back in...

That did it, the switch and voltmeter lit up. But still no AC power...

Duh, look under the sink-- the ship/shore switch was turned off! A flip of the switch and we were back to normal!

SO, it's possible it WAS putting out AC power in the first place since I forgot the main switch was off. But I'll never know for sure...

Regardless, it seems it was just a loose or dirty wire, as all I did to "fix it" was remove the switch cover. I gave all the wires and connectors a quick check, all looked fine, and she still worked fine after I buttoned everything up.

Many thanks!

2000 40' Tiffin Allegro Bus \ 2003 Chaparral 260 SSI
1988 53 x 14 Skipperliner \ 1995 32' Party Cruiser
1984 Goldwing Aspencade \ 1976 Harley Sportster
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