Diagnosing cylinder misfire

Dana67,

Having the dwell reduce with vac adv applied is good. Vac adv applied means cruise, which is low-med rpm where low dwell is better, because extra dwell is not needed & the coil runs cooler. High dwell is only needed for high rpm, to extend the charging time for the coil. The variable dwell of the GM HEI is one of the reasons it is such a good ign system: it keeps dwell low at lower rpms & extends dwell at high rpm where it is needed.