A whole bunch of engine-control sensors and actuators draw power from that fuse. One of them has its wiring frayed, and is shorting to ground. Or the device is defective and is drawing too much current.
First find out EXACTLY when the fuse blows. Is it when when power is turned on? If so, it's an easy troubleshoot, just follow the wiring and chase the short. Unplug the PCM if you're doing anything intrusive like attaching an ohmmeter.
Then use common sense. This will probably require going over the engine wiring harness with a fine tooth comb looking for defects.
If you're sure it's not wiring, then get a wiring diagram and a pile of fuses, unplug half the devices, try it, split the failing group in two and try again, keep going until it can only be one device. Replace.
It's remotely possible you have a blown PCM, but 99% of the time, if a mechanic thinks he has a bad PCM, he really hasn't done a good job troubleshooting. Mechanics love replacing $500 PCM's instead of $14 sensors.
Welcome to the new world of auto repairs. Scan tools and DVMs are the tools of the trade.
