Unfortunately I'm back again with what appears to be another electrical gremlin, and hopefully nothing worse.
Toward the end of last year's riding season I took my K75 out for one final ride before putting it in winter storage. I noticed the battery was very weak during startup, and made a mental note of replacing it soon. I rode one of my usual scenic routes but got stuck in an unexpected traffic jam. Making matters worse, my temperature warning light came on as I was inching through the gridlock. Every time the light came on, I'd shut off the bike and walk it for a bit. Eventually I was able to escape onto a side street and get enough airflow to keep the temp light off until I made it home. A few weeks later I installed a new battery but the bike would not start. Now that the weather is improving, I'm able to do some more investigating. I can get the bike to run (like crap) if I give it some throttle, but it occasionally backfires and blows a ton of black smoke that reeks of gasoline. If I let off the throttle it dies, and I don't run it like this for long because I'm sure it's wreaking havoc on the plugs.
Based on these symptoms and other posts I've been reading, it sounds like the coolant temp sensor is bad. However, I replaced it with a new OEM Bosch unit which didn't solve my issue. I checked the temp sensor wiring inside the sheathing and from what I can see, it looks new and undamaged, but I'm beginning to suspect it might be a wiring issue rather than the sensor itself. I also swapped in fresh plugs, new Bosch injectors, verified spark and fuel pressure, and checked that the air filter and airbox look clean. I have a spare computer that I hooked up, which had the same result.
Last season I replaced the Hall Effect sensor, so I don't think that's the issue (also those symptoms were distinctly different). I'm really hoping I didn't incur any engine damage from the brief moments it was running with the temperature light on, and the fact that it will fire up and run (albeit rich) gives me hope that's not the case. The overheating was a shock because I'd flushed the coolant and bled the system within the last year, and I've never had any cooling problems before, even in hot weather with lots of clutching. I'm thinking of acquiring a replacement sub-wiring harness but at this point I'm just throwing parts at it. Hoping to get your thoughts and recommendations on how to proceed given the details above. Thanks in advance!