I am lost for starters i replaced my catalytic converter w/a universal cat welded because it was clogged and wouldnt start i later found out do to engine misfire, cold started it ,it ran good for a while then engine started stumbling and shaking a lil, codes read bank 4 misfire then after a few revs multiple misfire code came up ce light started blinking. I installed spark plugs/wires in march. I also changed coil packs in early October (all 3) thinking that would solve issues but nope light started blinking again after a few revs of the engine followed by shaking. I haven't been driving it in fear of damaging the new converter because misfire issue still occurs where should i go from here¿????¿

 

Are there any codes other than misfire?
Is the cat compatable with the car? Check for the sticker above the radiator on the driver side. If it's a CA emission system it will say so.
Could also be a bad ignition control module or MAF sensor. Try unplugging the connector to the MAF with the engine running and check for difference.