Could the CDI be bad again?

[gregvhen]

ok well back in October i got a new CDI cause the old was blown. last time i was sure because once i hooked up the new the bike ran fine. well now its only running on one cylinder (right side).  spark plugs are good, wires are good, coils are good (even though i already ordered a new one anyway) but for some reason the left side wont spark.  i hooked up the ohm meter to the end of the positive and negitive wires for the left side coil, and they read basically no resistance all the way back to where they plug into the cdi, and i checked all the wires coming from the pick-up rotor up to the cdi and they were all good, almost no resistance. The gaps for the pick-ups are both good, and i hooked the ohm meter to check the resistance between the leads coming out of the CDI but i dont really know what that resistance should be, but i know it was the same for both the left and right coil terminals.  so is it possible for the CDI to fire one side but not the other? i assume yes, but i need a GS guru to tell me if thats the likely cause or not.

thanks, its a really stumper

Greg

[sledge]

My first thought would be a suspect sig-gen coil, failure of these is another common GS5 fault....have you tested and ruled them out? Unplug the smaller connector on the ignition module and go between the black/blue and brown and the black/blue and green/white. I cant remember the exact figure now (think its about 300 ohms) but it will be in the manuals.......both circuits should have a similar resistance.

Also, check out the auxilliary ground lead. Thats the small diameter black wire crimped into the battery negative lug. When this goes O/C all sorts of weird shaZam! can happen. First make sure it is actually crimped into the lug and the spade connecter further back on the lead is sound. Test it by pulling the plug from the reg/rect and checking for a circuit between the black/white wire in the plug and the battery negative terminal......it should be very close to 0 ohms. Or you can go across the battery + terminal and the black/white wire in the plug and expect to see 12 volts.

[sledge]

Been thinking about this......lets assume the ignition module does have 2 "seperate" trigger circuits, one for each cylinder, and that the circuit for the LH cylinder has indeed failed leaving only the RH circuit working.

I am thinking it might be possible to swap the trigger circuits contained in the module between the LH and RH cylinder by swapping over the inputs from the si-gen coils and the outputs to the coils. The module would still be operating what it sees as the RH circuit but because the signal is coming from the LH sig-gen and it is firing what it sees as the LH cylinder it would run on the LH cylinder instead of the RH cylinder and prove that the module is faulty. As the system doesnt feature a crank position sensor I am inclined to believe it might well work..although I wouldnt bet my mortgage on it and I am not prepared to try it on my own bike 

Looking at the wiring diagram and the module connections......

To swap the LH sig-gen with the RH would involve swapping the Brown with the Green/White and to swap the coil outputs would involve swapping the Black/Yellow with the white.

Anyone got any comments....OR willing to try it?

[bigfatcat]

I'd be inclined to doubt another cdi failure, assuming you replaced with a brandy-new oem Suki cdi .

My guess is wiring fault, oxidized connector or broken wire temporarily made good by you when replacing cdi.

I'd be looking for another gs owner nearby to borrow known good cdi for test comparison.

[gregvhen]

sledge, good thinking. ill try kind of that tommarow.  ill try hooking the right side wires to the left side output on the CDI and just hold a plug on side of the engine to see if i see a spark. and then put them to the right side again to make sure its fires this way too.  if i get a spark on both outputs then i know the left side wires are bad somewhere.  thanks sledge

[MattST]

Resurrecting this one because exactly the same has happened to me: twice.
Since I bought it the GS has had a new battery, new spark plugs, air filter, been serviced, brakes done, and a faulty indicator rewired.

The 'bike ('01 GS500) started firing only on the right cylinder. Limped to my local mechanics yard, whereupon the damn thing started firing on both cylinders again. Took it away, but barely made it down the street before it did it again, back to my mechanic.

He deduced it to be the carbs and after he did those, the 'bike started working again.

It worked for a three days (much better than before, to be fair) then back to running on the right cylinder.
Mechanic admitted to not bothering to check the CDi previously as he'd never seen one that had gone faulty before. He'd checked the coils and other wiring but not the CDi.
The CDi was melted on the side with the wires coming out and hot.

Ordered another off ebay. Fitted it under the watchful eye of my mechanic, fired it up, splendid!
Less than 2 miles away the 'bike went back to firing on the right cylinder only. Limped back to the yard. The CDi was not only hot, but black stuff was dripping out of a flap on the side where the wires come out.
It must be noted that the 'bike started faster after I installed the second CDi, the engine felt the best it ever had - could be because the carbs had been done too of course, but it was still a revelation.

Points that may give a clue to someone:
1. On the first CDi - the left cylinder stopped firing and stayed stopped until the 'bike had cooled down. It worked again after standing for about 10mins.
2. The temperature outside had dropped significantly the week I started having the problem.
3. The second CDi - when the left cylinder stopped working, as I limped back to base, every 30secs or so the left cylinder tried kicking in - I could feel the engine pull normally for a second (one cycle?). Did it about four times in the 1 mile back to his yard.

I can't afford another CDi 'til after Xmas, and I've decided I'm going to learn how to fix it myself (manual on it's way, I'll get a multimeter too).

I've still got the second CDi just in case I can get it to work since it's cooled down (like the first one seemed to do).

Any ideas?