Intermittent Non starter

[Motojim21]

2004 620 owned since new, I think it has 48k on it now. Service is up to date.
Usually the bike fires up fine, but randomly it will just crank won't start up. When this happens I can roll it down a hill in my garage and pop the clutch and it always starts this way.
I'm really at a loss with it. It's completely random but only happens on cold starts. The bike still has the immobilizer but the light goes out like normal when this happens.

[stopintime]

Hello,

random happenings are the worst... hard to diagnose because we never know when next time is. Bad connectors somewhere (!) can affect almost every function on the bike - including starts. Battery might be bad and/or draw so much electricity that there's not enough left for normal ECU function (possible or likely?)  Workshops/dealers can hook up their diagnostic tool to check all sensors and more. That might be a good start.

Have you done a search here? Find threads about "bad start" "can't start" "random issues" and that sort of topics. That can take some time, but is a great way to learn and to narrow down the number of suspects.

The good news is that since it only happens at cold starts, it probably is a somewhat limited number of issues to look for. Not EVERYTHING.

[Motojim21]

Thanks for the reply. Yes I've searched but haven't found anything with the same issue.

[Howie]

Start with fully charging your battery and getting it load tested.  Stopintime is correct that a battery can be strong enough for the starter to turn but drop below the voltage needed for the computer to be happy.  A shortcut would be if it starts with a jump.

Next step would be check the charging system and voltage drop in the starting circuit.  Do you have a multi meter and some electrical knowledge? 

[Motojim21]

Yes I know my way around a multimeter. Charging system is good, I'll see what the battery voltage drop is when cranking.
Thanks!

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[koko64]

Add a temp sensor to the check list.