Re: Grounding plug wires while checking compression
This is true of all engines with coils, be them magneto points, or CDI/solid state, you must provide a path for the spark or it will degrade the coils, condensor, and on electronic CDI systems. It damages the Power-Pack, or electronic ignition module as they are not designed to be back fed 20K volts from the coil when there is no spark plug gap to jump. We see condensors on old points systems go bad too, as well as coils from excessive cranking with no plugs...but the electronic pointless ignitions are the most susceptable and easily damaged. The funny thing is they will work intermitantly for some time when damaged and cause the engine to give you random fits that come and go, making troubleshooting often a difficult task.
Recently we have found on older engines using condensors that unless the condensor is bad, don't replace them. Why? Well because we have had more failures of condensors that were replaced during a tune up than any other ignition failure due to them being now made in Taiwan or China, and they don't hold up as well as the old Mallory, and Phelon USA made condensors.