Okay let's imagine i made it right with the ecu, coil pack,plugs,leads,the suspect injector, still have a miss on the 4rth cylinder, no compression test at the mo, anything else i'm missing?
not really, you need to do a compression test though. Its not uncommon for a cheap coil pack to drop a cylinder depending on the type, only other thoughts is a bad wiring connection somewhere
The coil packs are wired in series, so if you have a misfire on one cylinder, it will take out the other cylinder also on that coil pack. As you have a misfire only on one cylinder, your next move is a cylinder compression check. Disconnect your crankshaft sensor from the plug at the top/front of the engine, or unplug your coil packs. Check the compressions on all cylinders, they should all be around 150 p.s.i. Come back to us if you have more trouble after doing this.