B16A Starting problems

heres a good one...my 1990 Si with a B16A wont start...it sparks, it reeks of fuel when i'm trying to start it...so anyways, im pulling the plug to check the spark and it starts right up and runs on 3 cylinders...doesnt matter which plug we pull, it sparks and runs on 3 cylinders...but then we put the 4th one in and it wont start...then it idles really low...pr3 ecu, no codes...