I am trying to help a friend who bought a boat it has a Merc 150 hp (1997), I work on a few Evinrude & jonny's but not to many Merc in my part of world, Anyway the engine turns over just fine but has no spark, I checked both banks with a gap jump & light flash spark plug testers. no spark on any cylinder what should I check next? could there be a protection type of situation going on, low oil shut down, over rev switch etc. ? And if so is there a way to isolate the ignition to over ride this to test ignition components only? Any thoughts appreciated.