Join Date: Mar 2013
Location: In the twisties around Hendersonville, NC
K6 750 cranks but won't start. SOLVED
A guy posted up on FB about his K6 750 that just stopped running while riding. The starter cranks the engine but it does not run.
He had a previous issue with a fried ECM due to an overvoltage caused by an R/R installed by the previous owner. Boiled out battery as usual. But that was all fixed and bike ran well for months.
A shop had the bike for 2 1/2 months and had no success finally telling him that the ECM was probably bad again.
I offered to swap his ECM into my K6 to test but since he is about 50 miles away, we went through some tests over the phone first.
I had him double check for spark and there was none at any coil.
The cluster was flashing FI due to a C28 (secondaries removed) and a C46 fault but neither would cause the no run issue. Also temperature showed between the flashing FI. This confirms that the ECM is talking to the cluster and that is a good sign of ECM health.
The fuel also "primed" with key on which is also a good sign of ECM health.
I had him check for battery voltage at the spark coils and it was present so ignition and kill switch were good.
He makes the drive to my shop and we pop his ECM into my bike and it starts instantly. At least we now know it's not the ECM.
I reconfirm that there is voltage to the spark coil and also note that my test light does not flash on the ground side while the engine is cranked with the starter.
The conclusion is that the ECM is not triggering the coils and the usual reason is that it is not getting a signal from the crank position sensor (CKP).
I tested the CKP for resistance and peak voltage and both are within the service manual limits. Recalling several hot engine no run issues with no FI codes we pulled the clutch cover and found that one of the CKP mount screws was totally loose and stuck to the magnet near the coil sensor.
Loctited both screws, cover back on and the bike fired up instantly.
So this is another situation of a CKP problem not sending a good signal to the ECM but the ECM is not unhappy enough to throw a C12 code.
BTW, we did check with the CKP unplugged and after a few seconds of cranking, the C12 code popped up. I'm guessing that the ECM is only looking at coil resistance or some other low checks and not actually for a pulse.
"Riding well is difficult, riding poorly is easy and painful."
If you think reading is tricky, how the hell are you going to follow troubleshooting directions?
- Nick Ienatsch
"We're all here because we're not all there" - Guy Favron on Gold Rush