what are the common missfire problems other than plugs,coilpacks

engine recently had a rebuild and was running fine and then it melted a piston
due to some bafoon fitting a bleedvalve,and had turned right up

anyway i myself refitted engine and timing belt and when i 1st started it, it was running really lumpy (missfiring) so after fitting new plugs and testing coil packs (95 wrx ra) it was still not running right

so i was convinced i had the timing out so ave took belt off and made sure it is spot on but its still missfiring

anyone no what else it could be

 

could be fuelpump or maf m8

 

was a faulty coilpack

coil pack tests ok with a multimeter but still makes it missfire