My 550 lost spark suddenly last week. I ohmed the coil since it has 20 volt on both the 2 wires going in. The ground ohmed out to 0. I'm not sure how to test the coil. Then I heard that you can't. While working on it I randomly got spark back for 30 sec. I assume it's a coil but cant find on to swap it out with to make sure....any ideas or more tests I can do the right way.