No spark on the rear cylinder
 

hey guys, I need some help in finding out why my rear cylinder is not getting any spark, the from coils are giving good spark. I have tried to change the coils and its still not getting any spark. I checked the timing and its still onthe marker. Then I changed the ECU and same this. is there some ground wire I am missing because I just installed this engine and I paid a fortune. Any help will be appreciated