What Happens When A Cdi Goes Bad, And Why? - Snowmobile World : Your #1 Snowmobile Forum
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Old 02-26-2007, 05:24 AM   #1
WEATHERBY460
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on my yami, I lost spark completly and everthing else checks out ok. I am trying a new cdi this week. But was wondering why they go bad, and what are the sigh ns of a bad cdi?

Thanks
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Old 02-26-2007, 12:10 PM   #2
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Quote:
on my yami, I lost spark completly and everthing else checks out ok. I am trying a new cdi this week. But was wondering why they go bad, and what are the sigh ns of a bad cdi?

Thanks[/b]
When a CDI goes bad it is often due to mechanical failure triggering an electrical failure. Sometimes water gets into the electronics somewhere (even on models that are "potted" with ceramic or silicone) and either corrodes or shorts the electronics. One way that this can happen over time is if there is a spot on the wire harness that is frequently exposed to snow melt. Over time the copper wire actually wicks moisture through it by capillary action, until the moisture gets pulled all the way into the electronics. If you have ever cut open a wire harness and seen a copper wire that looks black in color for several feet or more, this is usually the result of moisture being pulled down the wire by capillary action. Some of the earlier T660 Arctic Cats failed cdis in exactly this way. There was a wire splice that had electrical tape over it but was not truly sealed. It would take a few months, but enough moisture would finally wick down the wire until it became a small almost-fountain inside the CDI. When you opened a failed CDI from this model it would have a lot of mineral residue spreading in a circle out from one particular pin.

Do visual inspections on wire harnesses whenever you get a chance to look for wear and water ingestion.

Other possible causes include a voltage spike finding it's way into the wire harness and following it into the CDI. This is sometimes caused when a spot in the wire harness that is laying against a sharp edge finally wears through and 2 wire short to each other, or the wire shorts to the frame.

As far as what occurs internally, most of the signals that a CDI uses are very low current and low voltage. Once the resistance of any part of the circuit changes due to corrosion or a short-circuit, the signals become unreadable.
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Old 02-26-2007, 05:03 PM   #3
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Thanks alot....that makes sense. I did find about 3 wires that could cause problems and repaired. So hopefully thats all it was.

Won't know for sure till the cdi comes in.
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Old 02-26-2007, 08:24 PM   #4
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I had the same problem.
Check your tether switches, kill switch, TORS (if still operational). Find the resistance readings for the magneto in your manual, and make sure those check out. Check your coil, but be wary, my manual was incorrect in the testing procedure...

Make sure you check all of your wires to see if they are connected, especially ground. Sounds stupid, thats what I thought...until I found that little wire hanging out of sight. Now I have a spare $60 CDI box...oops.


What was it doing when you lost spark? If it just died while you were riding, chances are its not a bad connection (although possible). If you worked on it and it doesn't spark now, DEFINATELY look at all connections and switches.
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Old 02-27-2007, 02:20 PM   #5
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Quote:
Make sure you check all of your wires to see if they are connected, especially ground. Sounds stupid, thats what I thought...until I found that little wire hanging out of sight. Now I have a spare $60 CDI box...oops.[/b]
Good catch. A lot of times electrical problems of all kinds are caused by a bad ground. Never take any ground for granted, also if you work on a sled put the grounds back exactly like the manufacturer had them unless you have expert knowledge to figure it out for yourself. Usually things are grounded a certain way for a reason.
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Old 02-28-2007, 08:23 PM   #6
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Quote:
on my yami, I lost spark completly and everthing else checks out ok. I am trying a new cdi this week. But was wondering why they go bad, and what are the sigh ns of a bad cdi?

Thanks[/b]
What I have found to be the culprit most of the time, is, a bad tail light socket. It shorts the power to ground and the cdi gets zapped! It's the first thing I look for on an old sled with cdi.
happy trails!
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