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Onan Nightmare


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#1 Harrelson74 OFFLINE  

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Posted September 16, 2010 - 09:39 AM

Need help with a P220V Onan engine. Replaced the following, all new; Ignition Control Module, Plugs, plug wires, flywheel key, and rebuilt the carburator. Will not start, backfires when I release the starter switch. Have no spark while cranking, but some spark when I release the starter switch. Any help?

#2 olcowhand ONLINE  

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Posted September 16, 2010 - 09:48 AM

So you replaced the pickup module at the crank? If you replaced the pickup & still no spark, it'll need the coil assembly. Only other part there is to replace. Long as there is constant 12VDC going to the coil, then it has to be the coil itself. Best whenever problems to just replace the trigger module & the coil both at same time.

#3 Harrelson74 OFFLINE  

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Posted September 16, 2010 - 02:01 PM

I have spark "after" I release the starter switch, for a second or two. Long enough for the engine to backfire. Coil checked out.
Thanks for the reply.

#4 NUTNDUN OFFLINE  

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Posted September 16, 2010 - 02:08 PM

Sounds like a bad ground or wiring is wrong from the switch to the coil or both.

#5 olcowhand ONLINE  

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Posted September 16, 2010 - 03:13 PM

Put a volt meter on the 12V side of the coil, then while cranking over, see that the voltage at the coil doesn't drop significantly.

#6 caseguy OFFLINE  

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Posted September 16, 2010 - 05:45 PM

I had a thought as I was reading this post. I know nothing about the engine in question, but if it is a multi-cylinder unit, is it possible for it to be out of time? Is it backfiring through the carb or the exhaust?

#7 Harrelson74 OFFLINE  

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Posted September 16, 2010 - 06:02 PM

Backfiring through carb and muffler. Timing is good. Thanks

#8 onan302 OFFLINE  

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Posted September 16, 2010 - 06:52 PM

Hmm sparking only when ignition switches off? Clean your points and check the gap between them.

#9 bhts OFFLINE  

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Posted September 16, 2010 - 07:14 PM

Sounds like a bad ground or wiring is wrong from the switch to the coil or both.


:ditto:

That would be my guess and a good place to start.I had a p218 do the same thing and it turned out being the key switch causing the problem.But i would check the grounds first and make sure you did not pinch a wire somewhere.

#10 olcowhand ONLINE  

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Posted September 16, 2010 - 07:37 PM

Hmm sparking only when ignition switches off? Clean your points and check the gap between them.


No points on the P series.

#11 jdslednut ONLINE  

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Posted September 16, 2010 - 09:57 PM

Hmm sparking only when ignition switches off? Clean your points and check the gap between them.


I swear I remember wiring a key switch wrong on a GT and having that happen.

#12 NUTNDUN OFFLINE  

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Posted September 17, 2010 - 07:18 AM

It will do that if the points are grounding out which this Onan doesn't have points or something else is grounding out when the switch is on, whether it is in the switch itself or somewhere else along the wires going to the coil or pickup.

#13 tractormike OFFLINE  

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Posted September 17, 2010 - 08:01 AM

I am not sure how your tractor electrical system is wired but check on if there is 12 volts to the coil when you let up on the switch "run position" and also when you are cranking the engine over. In some electrical systems 12 volts to the coil/ignition is supplied by the starter solenoid while it is engaged and the starter is turning. If that is the case and the solenoid is bad or the wire from the solenoid to the coil/ignition is bad you wouldn't have spark while cranking but could have spark when you let off of the switch from cranking to run position.

#14 massey driver OFFLINE  

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Posted September 17, 2010 - 08:01 AM

Can you maybe unplug the wire's to the switch and hot wire it,bypassing the switch to see if it will run.Just a thougth.Larry

#15 DH1 OFFLINE  

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Posted September 17, 2010 - 08:08 PM

Can you maybe unplug the wire's to the switch and hot wire it,bypassing the switch to see if it will run.Just a thougth.Larry


:ditto:

Or just take the wire off the coil that comes from the switch and put 12volts+ there and try it, see if it runs.




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