Hello,I have a 1996 mercruiser 5.7lt with thunderbolt ignition system.the boat sat for about 3 months,so I cleaned the carb and changed plugs,coil,rotor and cap.it was running fine untill recently and now I can't get it started.theirs power to the coil but no spark while cranking, it tries to start when I release the key on the ignition.i have gotten it started with this problem but it's hit or miss.would it be a faulty module?.I'd appreciate any input.thank you.