i have backfires from time to time (bout once a day) after i go WOT and then let off and shift. it doesnt really bother me at all but it does kinda tell me that i am running rich as poo. techtom showed all injectors pulse as just fine but both new o2 sensors are running rich at all times. oh well..you can lean it out with the afc, but i am not sure how you can with your custom thingy. i also assume your plugs are gapped down just a bit and are new.