YZ 250 2007 lost spark, ran diagnostics all good

L

Labradorcoaster

Evening folks,

lost spark recently, ran all the tests according to the shop manual. began at the plug, cap, primary and secondary coils, CDI magneto,pick up coil etc. All tested within the parameters shown in the manual. The advice given finally was to replace the CDI unit and run the tests again. I ordered a second hand CDi unit. Wondering if there is a way to test the old CDI.

Bike has low hours, seems strange for the spark to just up and leave...
 
2strokesteve89

2strokesteve89

Labradorcoaster:
Evening folks,

lost spark recently, ran all the tests according to the shop manual. began at the plug, cap, primary and secondary coils, CDI magneto,pick up coil etc. All tested within the parameters shown in the manual. The advice given finally was to replace the CDI unit and run the tests again. I ordered a second hand CDi unit. Wondering if there is a way to test the old CDI.

Bike has low hours, seems strange for the spark to just up and leave...
Click to expand...

The way I test them is I remove the module from the bike, put it on a clean work area, then I open my tool box drawer where I keep my multimeter, move it out of the way and grab my precision calibrated hammer. Then as I take carefull aim I strike the cdi dead center with a good hammer blow. If it breaks in two........its a bad part.
 
SRAD97750

SRAD97750

Moderator
Staff member
I have never seen a modern CDI fail. Ever.
I have picked up quite a few dead bikes on craigslist that , "need a CDI" and i get them running with a correct diagnosis. I would swap out every other component before even thinking about a solid state device failing.

Also, some components can test good, but not actually work under a load.

Good luck, electrical troubleshooting is never fun. -BIG DAN:thumb:
 
O

ossagp

Labradorcoaster:
Evening folks,

lost spark recently, ran all the tests according to the shop manual. began at the plug, cap, primary and secondary coils, CDI magneto,pick up coil etc. All tested within the parameters shown in the manual. The advice given finally was to replace the CDI unit and run the tests again. I ordered a second hand CDi unit. Wondering if there is a way to test the old CDI.

Bike has low hours, seems strange for the spark to just up and leave...
Click to expand...

I don't know of a way to test the cdi. Almost all of the manuals tell you to test with a known functioning CDI in order to test it. They seldom fail. Interesting, is that race teams replace the wiring harnesses often, and the CDI SELDOM. I think I would be doing continuity tests on all the harnesses, cleaning grounds and again, the kill button would be disconnected during that. (Ossa has the worst luck with kill switches of any kind. about 50 years worth of it.)
 
2strokesteve89

2strokesteve89

ossagp:
I don't know of a way to test the cdi. Almost all of the manuals tell you to test with a known functioning CDI in order to test it. They seldom fail. Interesting, is that race teams replace the wiring harnesses often, and the CDI SELDOM. I think I would be doing continuity tests on all the harnesses, cleaning grounds and again, the kill button would be disconnected during that. (Ossa has the worst luck with kill switches of any kind. about 50 years worth of it.)
Click to expand...

Resistance tests in my opinion are only worth their while if a circuit tests open or shorted, when testing any ignition module, the best way is check all circuits, powers, grounds,and signal circuits live. I've seen to many resistance checks lie, you can have one strand of a wire show good resistance, put a load on it and the circuit fails.
 
2strokesteve89

2strokesteve89

PawPaw:
OHMs test of the coil are very reliable.

Paw Paw
Click to expand...

Of all the coils I've condemned, none have failed an ohm test,and I've also replaced good coils that have failed an ohm test. This is all in the automotive world though. I test em like I said though, if there is power on the primary positive, and a signal from the ground, no spark from the coil, that's good enough for me.
 
2strokesteve89

2strokesteve89

PawPaw:
I stand by what I said, but would add that they have to be tested correctly.

Paw Paw
Click to expand...

As will I.....but I would add, If I failed a coil with an ohm meter, I would back it up with the tests I refered to above. plus I don't know anybody who has never replaced a good part, but if I test it a couple different ways and not rely on one test that some 4 eyed pencil protected engineer came up with, then I'm more comfortable with my diagnosis. But too each they're own, I'm only speaking from my 30 years of field experience and am in no way telling you your wrong, go with what your familiar and comfortable with.
 
O

ossagp

Steve, I am not sure what meter you are using, but my cheap meters show a difference when testing for continuity on a harness. The ones I test on a motorcycle are easy! The ones on a tanker or tractor and semi make you a little more resourceful. (Ask me to show you a shop made "test plug". Sometime.)15 years ago the industry made it possible for someone to troubleshoot without needing to know how to build one.
 
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