Yamaha TRX850 Enthusiasts Forum

Hello all,

Ive posted abit in the wanted section as im after a CDI box as i believe mine has packed up, wanted to know a few things first though please.

1) Can CDI's fail on just 1 pin?? Wont tell the whole story as it goes on forever and has caused me no end of grief but basically ive done loads of testing and the end result is that the grey wire coming from the CDI to the right hand coil isnt providing power and only the left hand coil is sparking (orange). When both coils are fired using the orange wire they work, when both coils are fired using the grey wire they dont work...all winding readings, caps, leads are identical and as they should be and plugs are spanking new. This leads me to believe that its the CDI but thought the whole box would go down not just 1 connection pin.

2) Do all UK trx's use the same CDI box, theres one on ebay if i cant get one on here but need to know for sure before commiting to buy.

Look foward to your opinions.

4un is the euro one 4nx gets you a restricted Japanese one, incidentally if you just want one to prove it's the box you can borrow my 4nx it works but is restricted to 7500rpm in all gears, scary when overtaking. Let me know if you need it

That would be tops bud, top bloody man!!

If you can post it to me please i will send some dosh back with it when im done to cover postage, will PM you now with my addy.
Would be great to be 100% sure before buying but i cant see what else it can be.

Electronics, baah...

Unfortunately I can't say if the CDI can fail like that, but I can support you morally

I would have done the same testing, and I would come to the same conclusion! But it's a good idea to test another working CDI.

So have you actually haven't illiminated the grey wire from the loom itself being the problem ??? Have you run some sort of test down the grey line from the terminal block to the coil to see if that may be the culprit itself???? ah har the plott thicken.ha ha ha ha ha ha ha..look out he's got a screwdriver oh no aaahhhhhh....

or is that just my illiteracy in winding readings????

Ive tried absolutely everything my friend and the only variable is the grey wire. When both coils/leads/end caps/plugs are used with the orange wire(left coil) they spark, when used with the grey wire (right coil) they dont spark. The grey wire shows continuity of 0.02 ohms so theres no breaks in the wire itself and all earths are good and cleaned up, cant be the kill switch wiring as the left coil/orange wire wouldnt be working??

So that leads me to believe that its the cdi box, the only thing is when i tested for voltage at the coils with the ignition on the right coil/grey wire was showing 12 volts......thats why im not 100% sure but cant understand WTF else it could be. Hoping another cdi will highlight something but if not then im screwed.

Electronic bugs suck.

Just an update, had a brainwave before going to work that i think confirms its the CDI unit but dont quote me.
Left the feed wires to the coils as they should be, orange to left and grey to right, but swapped them over at the cdi connector block so that the grey wire goes into the orange terminal and vice versa. On cranking the engine the right coil with grey wire sparked and the left coil with orange wire didnt (which always has previous to this swap)!!!!
This must surely mean that if the grey wire has no breaks and shows good continuity readings that the terminal pin where the grey wire usually connects too is faulty. Answers on a postcard to the usual address please.

hang on ,,, what about the pickup on the crank ?

What about it????? Dont leave me hanging.

Checked it to what the haynes said and it was a good middle of the road reading.

so both wires are showing continuity and you checked the pickup ,,it sounds like you are right about the cdi , there's only one way to find out ,, fresh one

Is there anyway that the kill switch at the side stand could be fouled, it's in a bugger of a spot to pick up road grime, chain lube. Also dont trust "new" spark plugs, they can be faulty. hope all goes well, and you get your bike running asap

trxster wrote:Is there anyway that the kill switch at the side stand could be fouled, it's in a bugger of a spot to pick up road grime, chain lube. Also dont trust "new" spark plugs, they can be faulty. hope all goes well, and you get your bike running asap

He wouldn't have spark on one pot then, surely?

Thats exactly my thoughts too idl, i kinda eliminated kill switches a while back. Firstly its not been on the road for over a year and was spotless to start with and a kill switch is designed to do just that...kill the entire system, wouldnt let one side fire up and not t'other.

Steve - i tested the pickup coil as the book said with the meter probes across the connector block (green/white wire and blue/yellow wire) and i got a good reading of 238 ohms....says it can be 192 to 288 ohms. Also checked the wires end to end for continuity and its good, both wires show 0.02/0.03 ohms.

Hopefully i wont miss out on the box on ebay while im waiting for the very kind mr glyn's cdi to come, cant see it being anything else apart from the cdi now after all this testing so might just bite the bullet and buy the thing. Seeing as theyre rare might be worth having a spare anyway.

i think your bang on ,,,its the cdi

To hear someone say that Steve is a beautiful thing, has driven me to almost insanity....well at least a higher level than normal!!!!

Cheers for all your help, thoughts, comments etc. Will let you know the outcome of the next stages.