Renault

Hi all ive bought anengine for my megane 1.6 8 valve after spending the best part of a day fitting it then discovered thr head gasket was away (enginr came from a renault dealer) but anyway ive now done the head on it its now running like bag of bolts on 3 cylinders ive set the timming up 3 times to no avail anybody have any suggestions i got the head skimmed and pressure tested as well so its not the head

Have you checked the injectors try using a long handled screw driver to locate the faulty cylinder.