OK, I am back with some good news.
I managed to get the RPM, I think the reason that the engine misfired was some code / repeated messaging.
I connected all my arduino circuits and tried to read the 0x7DF. and it sent out a response through 0x7E8 but with a general failure response 0x7F in the 2nd byte.
I then tried to connect the "Torque" android app along with my circuit and everything started working. Probably there is some command that I need to isolate for OBD2 to start responding to the request to 0X7DF.
I have dumped a before and after log, I will compare both and let you know the findings..
Regards,
Sathya