Mercury - Ignition Coil, 3.0L DFI OptiMax Ignition System 8M0077473. Overview. Anyone who's spent time around a 3.0L OptiMax knows they run great when the ignition system is healthy-and not so great when a coil starts to fade. These engines don't hide it either. You'll get a shaky idle, a cylinder dropping out as soon as you throttle up, or that mushy, uneven pull that tells you spark isn't keeping up. This coil is the proper OEM replacement for the 3.0L DFI OptiMax and several Mercury/Mariner t