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Discussion Starter · #1 ·
So starting yesterday the bike is misfiring from idle-5.5k. Changed the plugs, and it ran fine for 10 miles, went to ride it today and its missing again, though not as bad. I'm thinking its a bad coil, one of them looked a lil funky when I pulled them. Kinda hoping its not a valve. Any ideas?
 

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Coils and wires on a coil-on plug setup? If it's a coil/wire system a wire arcing to the head is very possible. Start the bike in a dark garage and see if you can spot any arcing. Sometimes if you cover the exhaust you can hear the "snap" of an arc as well.

This can happen to COPs as well, but then it's impossible to see. If you pull them and one is very dirty/gunky, it's a hint. Cleaning them can help, as does just wrapping the tube in a couple layers of electrical tape. If that solves the problem I'd pick up a new set, they're all over ebay for cheap. If yours have the mitsubishi logo on them, they're a lot more prone to failure, I'd replace them with Denso's. 99% of coil sticks have the same physical dimensions and very close resistances, close enough it doesn't make any difference.
 

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Discussion Starter · #3 ·
Yeah its a c.o.p. With resistor plugs. Also shoul note the bike has a danmoto carbon gp can and I gutted the cat.
 

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Measure the primary and secondary resistances of the coils. IIRC primary is ohms across the two pins in the connector, and secondary is between one of the pins and the plug terminal. Your service manual should give a spec for this, but measure all four and see if one is considerably different from the rest.

You can do the old school test and pull the plugs, stick them in the coil, and rest it against the head while cranking to see if all four plugs have a strong blue spark. If it's orange-ish in color, it's weak and may not be firing when under pressure in the cylinder.
 

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Discussion Starter · #5 ·
Its efi, wont the oldschool method fry electronics?? It is a bad coil btw, used a thermal imaging camera and swapped the coils around. First, #4 cylinder was cold, swapped the coil from #4 to cylinder #1, then cylinder #1 was cooler. My interpretation is that the coil is bad(the one from #4)
 

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I would stick with the assumption that that coils bad if thermal is popping up that way. it's an easy enough of a swap, I'd go for it. And probably clean up your plugs again while you're at it
 

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No, it won't hurt anything, I've done it with COPs on efi bikes. It's actually pretty tough to cook an EFI box, they can tolerate a wide range of conditions outside what they're intended to function at, and aside from some of the earlier ones, are smart enough to detect when they're being overloaded and just shut off power to that driver which usually trips the FI light.

But yeah if the misfire follows that one coil chances are it's toast. They're around $100 each from a dealership, I've bought a couple sets of 4 on ebay for ~$25.
 
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