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Is the coil going bad?


MathDude's Avatar
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04-03-18, 05:09 PM   #1  
Is the coil going bad?

I recently got a riding mower running again. I got a new carb and fixed the belts and it ran. It just wouldnít turn off though so I got a new key switch and it ran and turned off. Now it wonít start most of the time. Or it will start and then it will turn off on itís own and it wonít start. Or it will run and then die on itís own and not start. When itís not starting thereís no spark. Also sometimes when running it runs ruff and then may turn off or it starts running better. Seems to have spark sometimes and sometimes it doesnít. The coil is original from 2006 and it did sit outside for a few years.

Do coils go bad by working and then not working at times? I thought when they go bad they just quit and are dead. Is that not right?

Itís a MTD riding mower if that matters.

Thanks for the help

 
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marbobj's Avatar
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04-03-18, 05:24 PM   #2  
Post the engine make and model. that's helps a lot in diagnosing.

Coils can go south in varying degrees. A lot of times they work well when cold, then act up when heat ramps up the resistance in the coil winding.

It may be the coil/module or some other like a safety switch. A good way to isolate the problem is to disconnect the small kill wire that connects the coil to the wiring, which goes up to the kill switch. If you still have no spark the coil is likely the problem. If you get a running engine with it disconnected, the problem could be in safety switches or the ignition switch or some ground wires.

 
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04-03-18, 05:24 PM   #3  
In my experiences with coils that were failing, they started acting up once they heated up, so yes, it seems that could be your culprit. But there are other possible components too. You mentioned changing the switch, so I would go back to that, check all of the positions with an ohmmeter, make sure that the right terminals are connecting or not connecting. You will want a wiring schematic for this, which is often in the owners manual, or you may be able to download one from the manufacturer's site. Also check the safety switches for the blades, seat, and clutch or transmission to make sure they are functioning properly. If everything else checks out, and you're certain that you're not getting spark, I would go back to the coil. Others likely will have other or additional advice, so in the meantime you may also want to post the make and model of your machine, as well as the engine.

 
MathDude's Avatar
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04-03-18, 05:37 PM   #4  
Thanks for the help. Iíll test the switch to see continuity and Iíll unplug that wire that goes to the coil to kill it and see if it sparks.

Just making sure...when I unplug that wire from the coil...if thereís no spark...then the coil should be bad, right?

 
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04-03-18, 05:40 PM   #5  
Model info attached. Sorry about that.

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marbobj's Avatar
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04-03-18, 07:41 PM   #6  
Usually if the engine is running, then dies with no spark and you disconnect the kill wire and still no spark you have a bad coil. But the check for spark has to be between the coil and a good ground. If using a spark plug in that circuit, you have to have a known good plug. It's better to check in a garage, rather than outside where the spark is harder to see.

What you're doing by disconnecting the kill wire is to isolate the coil from all other circuits.

 
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