I have a 1995 Mariner 200 magnum EFI that i just lost a piston in. I was running the engine at WOT on the boat when the RPM's dropped about 300 to 400. I checked out plugs and discovered a burnt piston that i replaced the next day. I ran the engine again at a lower RPM and rechecked plugs, but the same cylinder is running leaner than the rest! What would cause this on a EFI? Bad injector maybe?
