You have a short circuit in the PCM circuit, but it can be a power wire shorted to ground or an internal short in one of the electrical components in the circuit.
Try disconnecting the electrical components on the circuit one at a time, and see if the fuse continues to blow. When you remove a part (pcm, relay, etc) and the fuse stops blowing you have started to narrow down your short circuit.
Then examine the wiring in the circuit for places where the wire may be rubbing on a piece of metal, causing the short circuit.
You should have a wiring diagram to perform this type of diagnosis, try here for a good one: http://bit.ly/mitchell_repair_manuals_online