Hello and welcome to Just Answer!
The ECMb fuse supplies power to the ECM and the fuel pump. What we see most often is as the fuel pump wears out, the amperage draw for the pump will increase. Eventually the amperage exceeds the fuse capacity and it blows. Most of the time the pump will outright fail before this happens, but not always. It's very unlikely for the ECM to be drawing enough current to blow the fuse as 20 amps to the ECM would destroy it.
The only way to know for sure is to use a lab scope with an amp probe to measure the current draw from the fuel pump. remove the fuel pump relay and install a jumper wire to run the pump and clamp the low amp probe around that jumper wire. That pump should draw about 6 to 8 amps.
In my personal experience the fuel pump is almost always the culprit when the ECMb fuse blows.
thanks and let me know if you need anything else.