There are a handfull of circuits that come off of the ECM-B fuse, so you will need to inspect the wiring from the fuse box to the ECM, to the oil pressure switch and back to the fuel tank. You will need to look for places where the harness can rub on something or is being pinched by something.
If a visual inspection does not reveal anything, you may want to drop the tank and look at the fuel pump (the main component on this circuit). This is the #1 cause for ECM-B fuses blowing, but don't overlook the obvious before you drop the fuel tank. Either the pump goes bad and pulls excessive amperage, or the wires going from the sending unit to the pump melt together causing a short circuit.
Please let me know if you have additional questions!