400EX has no spark and cant figure out why! - ATVConnection.com ATV Enthusiast Community

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Old 09-03-2017, 02:51 PM
Weekend Warrior
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Join Date: Sep 2016
Location: central illinois
Posts: 2
Default 400EX has no spark and cant figure out why!

Got a 04 400ex that has no spark. Been trying to figure out what is wrong with it for about 6 months now. I have replaced the stator, cdi, rectifier, the stator pickup, and coil. I have stripped my wiring harness to check if there were any broken wires. Nothing wrong with main harness or the start/kill/light switch that I can see. Tried a few things I've seen on forums. I don't know what else it could be. I'm stumped and I have worked on multiple 400exs and never have had this problem before. If anyone could help me out, that would be great.
Thanks, Cody
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Old 09-04-2017, 02:21 AM
Pro Rider
Join Date: Oct 2013
Location: Lancaster England
Posts: 2,633

The trouble with the substitution method of fault finding is, if you fit a new component that is a "dud" you have introduced another fault, so even if you cure the original fault by substituting the first faulty component with a good one, you now have another fault preventing the machine from starting. Best practice is to check the circuit at the CDI using the fault checking list in the manual, and if doing substitution, put the old component back on if the new one doesn't fix the problem.
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Old 10-12-2017, 08:34 PM
Weekend Warrior
Join Date: Oct 2017
Posts: 1

I'm having the same problem got no spark on my 07 400ex. I put a new spark plug , coil pack , kill switch , cdi , and air filter but that was just to accommodate the cdi boxes needs and I still have no spark but I think the cdi is a dud because the one I got for my 250 will try to start my 400 where as the oem and aftermarket ones will just keep cranking over.
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Old 10-13-2017, 12:57 PM
DirtDevil101's Avatar
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Join Date: Oct 2015
Posts: 974

do you know how to use an ohm/voltage meter? If not time to learn! They are cheap and will help you identify the fault...

You'll start at the stator and work your way up. Make sure your ground is on clean BARE metal!!!
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