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Onan Generators

Another Onan "won't start" Thread...


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  #11  
Old 04-17-2018, 05:28:31 PM
Kevin K Kevin K is offline
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Default Re: Another Onan "won't start" Thread...

The voltage regulator does not prevent spark, with the exception that if the rotor is not flashed correctly and no output voltage is produced the set will shut down when the start switch is released.

When the start switch is pressed, the control board applies 12 volts to pin P2-3 then to voltage regulator pin 7. The voltage regulator passes the 12 volts to pin 9, then to the positive rotor brush to flash the field. When the start switch is released 12 volts battery voltage is no longer applied to those pins.

When the start switch is pressed, ground is removed from control board pin P2-4 (ignition enable output) allowing the magneto and coil to produce spark as long as the low oil sensor (if any) indicates enough oil to run.

If you want to check a no spark condition do the following: Insert an inline spark tester between the spark plug and the spark plug lead. Remove pin P2-4 from the control board harness connector. This pin is grounded when the control board shuts down the spark. By removing this connection, the control board will not be able to shut down the spark. Disconnect the low oil sensor if one is used. Crank the engine and verify spark at the spark tester. If no spark is being produced, the coil or the magneto is defective. If a spark is produced, the magneto and coil are OK.
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  #12  
Old 04-17-2018, 07:49:26 PM
Frankshay Frankshay is offline
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Default Re: Another Onan "won't start" Thread...

Hi Kevin, thanks for your remarks. I've been checking for spark by holding the plug against a ground on the engine but I really should get an inline tester. I'll remove P2-4 and see if that does anything (oil level switch has previously been disconnected).

Do you think it makes a difference if the spark plug is a resistor type or not?

thanks,
Frank
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  #13  
Old 04-18-2018, 05:58:24 AM
Kevin K Kevin K is offline
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Default Re: Another Onan "won't start" Thread...

You should see no difference between a resistor and non resistor spark plug, but I would stick with the recommended plug.
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  #14  
Old 04-21-2018, 01:45:24 PM
Frankshay Frankshay is offline
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Default Re: Another Onan "won't start" Thread...

Quote:
Originally Posted by Kevin K View Post
If you want to check a no spark condition do the following: Insert an inline spark tester between the spark plug and the spark plug lead. Remove pin P2-4 from the control board harness connector. This pin is grounded when the control board shuts down the spark. By removing this connection, the control board will not be able to shut down the spark. Disconnect the low oil sensor if one is used. Crank the engine and verify spark at the spark tester. If no spark is being produced, the coil or the magneto is defective. If a spark is produced, the magneto and coil are OK.
I removed P2-4 from the circuit and with new coil and spark plug do not observe a spark when cranking. This points to the magneto I guess.

Does anyone have any hints about accessing the magneto on this unit? I guess I'm looking for "how to" type of help. The service manual discusses testing but offers precious little about disassembly.
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  #15  
Old 04-23-2018, 05:11:26 PM
Frankshay Frankshay is offline
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Default Re: Another Onan "won't start" Thread...

I just ordered a new magneto. The wire between the magneto and coil has continuity and the magnets are of course still very strong.

For some strange reason you have to remove the generator endbell to access the magneto screws. It looks like this could be accessible w/o having to remove the endbell if the bolt/screw heads were on the outside instead of the inside. I won't know until I take this next step however.
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  #16  
Old 04-26-2018, 07:21:38 PM
Frankshay Frankshay is offline
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Default Re: Another Onan "won't start" Thread...

(cue happy dance)

The new magneto did the trick, how sweet it is to see that bright blue spark! And now I have a spare coil. Like many machines, once you have it apart the instructions make sense. It starts right up and sounds as good as ever. Thanks for folks' help on this one.
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