I have a 1997, 40 HP Johnson that loses all spark from time to time. Sometime it works great and will crank right up while other times it just will not fire (no spark). I suspect that the power pack is bad since I've checked the ground circuit (black/yellow wire) and I've checked the resistance on the ignition coils and sensor coils. I thought that these electornic power packs either worked are they don't. Is it unusual for one to work sometime and not work other times. It seems to stop working after it sets up for a week or so. Has anyone seen this type of problem before? Thanks.