Diagnostic tests revealing errors inherent in the ignition coils have shown that in some rare cases it is possible that the ignition coils in question (dating from before 2009) damage the engine control unit (PCM).
This type of fault may be imputed to a short-circuit between the ignition coil 12 V power supply and the coil electronic ignition circuit.
To check whether the PCM has been damaged, check the resistance between the PCM module connector pins B1 and C24 (if the PCM is NOT damaged there MUST be continuity).
In any case check that all the coils are operating correctly.
Before replacing the PCM we recommend you contact an authorized Mercury/Mariner assistance service