At some point there was a weak or lost ground from the ECU to the engine. This can cause the ignition coil's built in driver to overheat and short in a way that causes the input of the driver to short to the output, which is the negative side of the coil's primary. At this point as the ECU's output tries to drive the coil's input low and it "sees" +12v through the coil's primary, which has a resistance of about 1 ohm. The ECU's coil output pin is now trying to switch over 10 amps to ground. The battery wins and smokes the ECU's driver which is only rated for 0.05 A. The driver is part of an IC that has about 30 other channels. That coil channel will be blown for sure but usually some other's are as well, but in a random pattern that is not always the same. Some of the other I/O channels; CAN, fuel pump, OBD2...etc. Even when the ECU's ground is restored the shorted coil(s) remain and if a new ECU is installed and powered on the same damage happens again. Unplug all of the coils from the harness and try another
ECU.
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