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Discussion Starter #1 (Edited)
Hi all,

Have tried working through an electrical issue for some time now. A few months back my 2017 350 exc-f would not restart after I stopped. So I would ride, hit the kill switch and then go to restart moments later and nothing. After waiting a few minutes it would then fire and not miss a beat. It then started cutting out when riding, and again wait a few minutes, restarted and away I went. I went home to work on it but could not replicate the problem, was running fine. I replaced the spark plug and cleaned out any connection I thought may cause an issue.

I then rode the bike for 5-10 hours without any missing / cut outs. I also stop by kill switch or stall, it restarted and ran no worries. Couple weeks after I was 2 x half hour laps into an enduro, I went to start my third lap and the bike would not restart. So this time I had it in my garage not running, I checked for spark and nothing. Also noticed the speedo dispaly does not light up / work when trying to start bike.

Started resistance tests, only thing that was out of spec was the spark plug lead and cap, rescrewed together and resistance went back to normal but still not spark or speedo display. Checked small fuse box under seat, all ok. Checked main fuse with the relay and ok. At this point I borrowed my brothers 350, changed over:

- coil
- ecu
- volt regulator
- spark plug
- spark plug lead and cap
- relay
- battery
- tripple checked kill switches
- tip over sensor

After all this still nothing and I fitter all my parts to brothers bike and his bike started. I removed the switch type kill switch, no difference. This is where it gets coincidental and annoying. I swapped the stators over, and then my bike started :wink2:. Brothers bike did not start with mine in it. I then swapped stators back to original bikes thinking I found the problem and to hand his bike back. But I then realised I should make sure then isn't just a dodgy connection as stator is not that old... and are expensive… So hanging of the stator is a what ktm call a pulse generator, which to me looks like a timing sensor picking up tabs on the flywheel. After a few more checks it seemed like this was the problem, I doggied up my brother pulse generator with my stator and bike had spark and display back.

Unfortunately ktm dont sell the pulse generators separately, so would still need to by the stator. I went double checking it wasn't connections again and put all back together with original parts just to close engines back up for the day.... then both bikes worked.... :|:|:|

So my guess is a dodgy connection. I then started point to point testing each cable and could not get a resistance increase when wiggling and bending around cables / connections. Left it at that and rode it. Rode for another 5-10 hours, does not miss or anything, then stopped at a point on the track to regather the group and would not restart. I towed it back and had bought a spare stator with pulse generator as thought they may be packing it in with heat. Replaced with the new and still no spark or speedo display. Back to the garage and swapped:

- coil again
- speedo unit

Both of brothers bike parts did not start my, but both mine started his. So back to the drawing board. Checking connections again further up stream i guess. :hammer::hammer:

Any suggestions??? :surrender::surrender:
 

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Painful diagnosis

I can feel your pain on this mess you have here
Troubles like this are like a throbbing pain in the balls:frown2: good on you for your diligent and sensible diagnosis and persistance. I studied your post and troubles and testing and would offer a few ideas from my own experience. First off worth mention is both failures on your bike are magnetic triggered components. Speedo and ignition trigger are magnetic triggered and possibly upset by voltage spikes. My observation from numerous no start conditions on my own and other bikes when cranking the starter current draw causes a slight flux near the ignition trigger and confuses spark timing to cause engine to refuse to start until kill switch is tapped when cranking. The momentary grounding of ignition circuit seems to reset ignition and motor fires immediately after tapping kill switch. Not sure this is your issue, but worth a try. Also worth checking is individual wire connection at plug connectors. I have seen the brass pin terminals crimped onto the insulated part of the wire instead of the wire itself. The connector crimp punctured the insulation enough to contact copper wire inside but could not carry current for extended periods due to limited contact and higher resistance of connection. It seems these connectors could have been stripped or set incorrectly and test good but won’t make secure connection afterwards. Removing pins from plug connector for inspection can sometimes uncover defect. I have seen plenty of complete wiring harness replaced for this exact problem. Very difficult to detect and resistance testing is not always reliable.
 

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Discussion Starter #3
Thanks! Will definitely give these a go. It has been a battle but want to see it out a bit longer before retiring to a shop.
 

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Discussion Starter #4
Found the problem after a bunch of other things like TPS, connections etc.

It was a faulty power relay that was not switching to provide 12V to the speedo and couple of other things. It is one of the two relays that sit in the air box. Took it out and tested on the bench to make sure it wasn't a dodgy connection, put 12V across it and started working then stopped, then started... intermittent... just like the problem was in the first place.

Anyway will order another and get going. So if you have a no spark problem with also a blank speedo display it could be this power relay.
 

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I have been searching the web for something, anything that describes the issue on my bike and I think this is it. I’m on a 2004 KTM 525 exc that exhibits the same erratic loss of electrical power but other wise in great working order. I did change the power relay but the issue is still present. My other suspicion is a bad earth but I earths look good. So frustrating!! To me it has to be the relay for current to just stop don’t you think. Voltage spike is an interesting concept. Any more help out there?

Thanks
Brad
 
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