Car had been running fine for nearly two years (M94 STi import) and in February I had a coil pack failure, it was running rough on 3 cylinders, didn't have time to do it myself at the time so i took it to my local garage, he fitted a used coil pack, a Diamond 22433AA330. This again began to fail on me, not completely, but poped and backfired under full boost, ran perfectly driving the car normally. I then got hold of another used coil pack, fitted it and it ran perfect for a week, then caused the same symptoms under full boost. The other three coil packs are a different make to the Diamond part, with a different serial number. Would I need to get an exact same coil pack as the other three or am I just unlucky with the two I've had fitted as replacements?