Comparing Ciphertext when there is a change in source plaintext p1
i don't think that there is a way to check the changes on block cipher if you are using random IV here, since the IV will go to Enc first, then the output would be totally different than before, 

if you are using the same IV, then try to figure out the the block length for the block you are using, if it is 16 bytes, then change the first 16 bytes will result first 16 bytes of ciphertext to be different. Since before output the ciphertext, it is just a one-time pad. 

hope it helps.