The reason for Pakistan in trying to get hold of western engines is a sound one... First of all, Pakistan is flying lots of westerns birds - F16, Mirage and stuff like that. Thus the engineers and technicians are very familiar with the western engines and how to maintain them. Thus it is logical for the Pakistan to try to secure the western engines for their JF-17.
However given that the chinese engines for this class of fighters might be on par with whatever the Westerns are willing to offer and sell, I guess it would be easier for Pakistan to stick with the Chinese's.
Well officially PAF officials i believe have never said about an engine change, but they had talked about an avionics and radar option.
As for western engines, PAF has been using nearly an equal number or more of the Chinese engines also, as we have A-5, F-7Ps, F-7PGs, FT-series trainers, which become in hundreds. And the Chinese engines have been working good.
The only concern was the Russian factor, due to which talk of western came into being, as at that time Chinese option was not fully ready, but once Russia assured of no supply problems & China came into the picture, PAF is ok with RD-93 and recent news indicates a more powerful version would also be available.
But in the end, Chinese option is what suits PAF the best, operationally, maintenance wise and no strings attached policy, we can have an in house over hauling facility, which would speed up operational maintenance and cost saving compared to either Russian or Western options.
PAF is waiting for a Chinese option and the moment it becomes available, it will be used.