Ok we had our check engine light start flashing and took it to auto zone and they said it was mis firring and after changing plugs and wires next step we were told was to change coil pack. Changed it out and no difference. took it to a mechanic and found out it was the ecu. Had a new one put in and ran fine. Since the old coil pack was still good I called auto zone and they said we could return the new one. I swapped them out and when i started up the car it ran like crap. I put the new one back in and still runs like crap. Check engine light is flashing again and put it back on the tester and it comes up faulty cad converter caused by random misfire or something about ignition coil secondary number 3 circuit condition. detected erratic signal from the ignition coil. Any idea on what i may have done or how to fix it. Thanks in advance.