Well, this will get more hits if it was in the right section. (I'll move it to the merc section)
The Spark on the 240 is pretty simple, and the ECU doesn't really control it.
The kill switch is a simple ground sytem, and when it's "Open"... you get spark. When it's "Closed" (Grounded) it kills the spark. So... disconnect the black/yellow wire at the coil packs, and make sure it's not grounded.
The second part of the system is the trigger coils. Make sure they check ok.
If you lost spark on all the plugs... then I would be leaning toward:
1) Kill wire grounded. Either a bad lanyard, or chaffed wir
2) The dreaded throttle guardian has messed up. They suck, and I recommend removing it, if your boat has it. (assuming it's still there)
3) The control modual, or Rev-limiter gave up.
4) You lost power to the ignition unit.
The spark itself is a Mag system, and the coils charge via a high voltage coil in the stator. But, the rest of the electronics run on 12v. SO... grab a meter, and check for power.
