Hi All!

I'm trying to make an application for ELM327 trouble code scanning device for my own educational purpose. Most of my app code is done. however, I am stuck at one point. And I need someone to help me finding relationship between two hex strings.

I have logged some communication between ECU and a chinese code scanning device for carrying out car's fuel pressure test. However there is one message (that is sent from the user side) that keeps on changing each time which is dependent upon the last message received from the ECU which is also varying every time.
I'm posting different responses from logged data for carrying out fuel pressure test at different times.

Code:
RECEIVED (07E8)			     SEND (07E0)
05 67 03 0C 17 6A 00 00	     05 27 04 8F 45 37 00 00
05 67 03 0C DB 68 00 00	     05 27 04 B0 70 6B 00 00
05 67 03 10 3B 87 00 00	     05 27 04 3B BC 10 00 00
05 67 03 12 CC E7 00 00	     05 27 04 5A 50 5B 00 00
05 67 03 13 A4 88 00 00	     05 27 04 34 E7 63 00 00
05 67 03 15 D9 CB 00 00	     05 27 04 5D 76 7D 00 00
05 67 03 1A 2F 05 00 00	     05 27 04 57 81 33 00 00
05 67 03 1B 45 AE 00 00	     05 27 04 E8 10 E7 00 00
05 67 03 29 BC B3 00 00	     05 27 04 85 65 10 00 00
05 67 03 31 09 97 00 00	     05 27 04 E1 FB A6 00 00
05 67 03 32 C5 6B 00 00	     05 27 04 D1 EC 83 00 00
05 67 03 33 1E 9E 00 00	     05 27 04 7A A4 AF 00 00
05 67 03 3A F6 2F 00 00	     05 27 04 71 26 98 00 00
05 67 03 3B 75 AB 00 00	     05 27 04 E9 76 0C 00 00
05 67 03 3E 50 51 00 00	     05 27 04 59 2B 67 00 00
05 67 03 3F D9 94 00 00	     05 27 04 91 2B D3 00 00
05 67 03 42 58 A9 00 00	     05 27 04 19 E7 CB 00 00
05 67 03 43 F9 A0 00 00	     05 27 04 55 81 ED 00 00
05 67 03 48 82 DD 00 00	     05 27 04 F3 2D 41 00 00
05 67 03 4E 25 DE 00 00	     05 27 04 DE F2 99 00 00
05 67 03 51 40 DE 00 00	     05 27 04 DB B6 DF 00 00
as it can be seen 3 bytes are always changing with each test, both, in the message received from the ECU, and the one sent back to the ECU from the diagnostic scanner. Can anyone help me trying to figure out relationship between these two strings?

P.S: about 16 million combinations for 3 byte data are possible... there must be some link between them...