Why is this hash function (based on a block cipher) insecure?
If you want a hint as to why your proposed hash function isn't secure (even against preimage attacks), I would note that block ciphers are invertible, that is, given $C_{i-1}$ and $C_i$, we can efficiently compute the value $P_i$ must be so that $C_i = E_{C_{i-1}}(P_i)$ holds.  Question for you to complete the answer: how can an attacker exploit this to create preimages?