Ok, it has its own ground because the cossie normal ecu ground can vary
due to injector peak currents and wiring voltage drops in these conditions.
If there wasnt a seperate ground, the coil would missfire as the ground
of the ecu moves around 0.5volts during various conditions due to the trigger
signal being only a 5 volt (TTL) signal as is very suseptible to electrical
noise and disturbance.

Hope that explains things.


Simon