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Onan 4.0kW Generator has been sitting for at least 6 years


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  #1  
Old 04-14-2017, 05:53:34 PM
twitchee2 twitchee2 is offline
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Default Onan 4.0kW Generator has been sitting for at least 6 years

Hi guys, I have been doing quite a bit of reading on this forum trying to find the answer I and so far I have been striking out. First off, I apologize, I do not have my serial number for the generator right now. I will try to get it soon. Here is what I do know. It is an Emerald 1 Genset, I know it is a 4.0BGE Gas powered unit.

This is in a 1986 Winnebago that I recently picked up and this is one of things that is not working properly. I am a back yard gear head and I almost have the Ford 460 running right. Rebuilt card, new vac lines, all new ignition, full tune up etc.

I have narrowed it down to not getting fuel. The fuel pump was jammed up from not being used in a very long time. I unscrewed the bottom and free'd the plunger up. I can hook up a car battery to it directly and it pumps fuel just fine from the tank. I still will likely replace it, but it works well enough to get this thing operational.

I manually pumped fuel to the carb with the battery. If I hit the start switch and it will fire up and run until it runs out of fuel 5-10s, maybe. But after connecting everything back together, the fuel pump is not running. I am an engineer at an electronics manufacturer so I brought the old PCB in and had my failure analysis manager take a look at it. There is nothing obvious and all the components work properly.

I have studied the schematics for this unit as best I could but am not sure where to go from here. Where does this PCB get the signal to enable the fuel pump?

Thanks!
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Old 04-14-2017, 06:16:03 PM
len k len k is offline
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Need the full model and serial numbers.

But in general on the control board the same relay that powers the spark coil also sends power to the pump. But on some boards they put in a series diode with outputs. All diodes can easily blow if you short their output to ground.

Trace the wire from pump back to the board and see if you have power out of the board.
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Old 04-14-2017, 06:32:00 PM
twitchee2 twitchee2 is offline
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Quote:
Originally Posted by len k View Post
Need the full model and serial numbers.

But in general on the control board the same relay that powers the spark coil also sends power to the pump. But on some boards they put in a series diode with outputs. All diodes can easily blow if you short their output to ground.

Trace the wire from pump back to the board and see if you have power out of the board.
Will do that again. I actually did that and saw some funky voltage, almost an AC voltage. What should I expect? Solid ~13v voltage, Correct?
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Old 04-14-2017, 06:47:14 PM
len k len k is offline
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Voltage to pump or spark coil should be something like 10VDC to bat voltage.

If it's jumping around erratically it could be a bad connection, burnt relay contact, or just spark coil loading the line down as coil charges between firings.
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Old 04-14-2017, 08:30:32 PM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

I would suggest cleaning the GENERATOR slip rings BEFORE trying to get power out of it or running it for any length of time. I learned this from len k. This saves the voltage regulator from dying a quick death.
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Old 04-14-2017, 09:04:10 PM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Yes, if it's spec D or higher it has a $$$ electronic AC votlage reg that can die if gen sits for months and you don't clean slip rings before running.

10-15 seconds at no load is about the time it takes mine empty the carb bowl too , if pump is not reloading it with gas.

Last edited by len k; 04-14-2017 at 10:49:25 PM.
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Old 04-15-2017, 12:04:30 AM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

So I am very new when it comes to generators, is there a write up on how to get to the slip rings? I swung the generator down from the mounts, do I just take the cover off and clean the rings with some rubbing alcohol?

When I said I work for a electronics manufacturer, I should say we are a motion control company, I am very familiar with the inner workings on electric motors, etc.

Thanks!
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Old 04-15-2017, 02:00:15 AM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Take a piece of Scotchbrite and clean the slip rings. you can remove the spark plugs so it turns easy and fit an Allen wrench in the hex at the generator end to turn the generator rotor. I remove the brush block on my BGE to get better access but make sure the screws aren't seized in the threads and you break off the hold down screws. DON'T leave the generator hanging at a steep angle for a day or more. The crankcase oil can fill a cylinder and lock the engine.
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Old 04-15-2017, 12:32:33 PM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

Scotchbrite, no rubbing alcohol or liquids.

To clean mine I , made a tool from a kitchen fork. I ground off the side tines of a 4 tine fork, tied a strip of scotch brite to it, and held it under the slip rings. Didn't have to remove brush holder. I'm lazy so I let engine run, but I unplugged AC reg first to protect it. But my gen is a NHM, so it will run while not making AC. You'll have to crank engine, removing the spark plugs will be easier on the starter. I wouldn't crank it for more than 10 sec without letting starter cool ~ a minute.
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Old 04-15-2017, 01:30:31 PM
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Default Re: Onan 4.0kW generator has been sitting for atleast 6 years

I use a popsicle stick with scotchbrite taped to end.
If something goes wrong, and pad gets caught, stick will break with minimal damage to gen, and none to my hand.

No way am I holding a piece of metal near supposedly dead slip rings, or a commutator .
also, if metal get caught, may do damage to gen.
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