Rooster 192 #26 Posted July 16, 2012 When the right cylinder fires the left cylinder is half way up on compression. (90 deg V) I think what your real question is, what are the cylinders doing during the waste spark, which happens at the end of the exhaust stroke. Any idea if the diode(s) fail, do they fail by shorting out or opening up? yep...most commonly they short, bu i have seen them open. I assume if a diode opens up (electrically like someone cut the wire off the diode), the cylinder will stay alive when the ignition switch is turned off. A diode shorting out (becoming like a piece of wire) would cause the interference between the coils. Interesting. eggzactly Share this post Link to post Share on other sites