I got to find out first hand why you don’t want to buy cheap coils/packs. I was poor and needed to get an 03′ Taurus running, so I ordered a coil pack online for $26. It did fix my misfire at the time, but not even a year later I started getting some misfire, particularly at startup and eventually a “misfire on startup” code. After ruling out a few other things and scratching my head for a bit, I eventually decide to do another cylinder drop test, and lo and behold it had very weak spark at the coil.
Installed a quality pack and it runs like a champ! I learned from other’s mistakes not to rule out something just cuz it was recently replaced, now you can learn from my mistake of being a cheap ass :b