Hello to you. Pre and Post detonation are the result of raw fuel igniting prematurely or raw fuel going into the exhaust and igniting in the exhaust system. Thus, it sound like your have raw fuel dumping into the exhuast that is igniting causing the backfire. This can be a timing problem, a coil pack, plug wire, or plug that is going out or bad (thus not firing to ignite the fuel in the cylinder) and causing a miss. If you notice a rough idle, engine miss, check the plugs, look for one that is fouling, check the resistance in the wires, then check each of the two coil packs for a bad tower or split. In essence, you can simply pull the plug wires one at a time while it is running until there is NO change and that would give you the cylinder at fault, or you can tell us how many miles your timing belt has and if it has been replaced recently. (Like when the head gasket was done for the factory issue they had). If you supect the timing is the problem then pull the covers and align the timing larks and see if they are even one tooth off. If so correct it, if not, then check the tensioner and close it up. Either way, you are getting raw fuel into the exhaust system and thats where the popping is coming from.