ok this just happend to me a while back look at what i had to go through
i had to cut into my main harness all the way to inside the car, and just like you my car would blow the 20AMP engine fuse just like urs. ok so let me tell you what i did. i got a bulb to like a autometer gauge and put it in the socket where the fuse went( you gotta be crafty) find a way to do it. so i connected the wires to the burnt out fuse than stuck the fuse back in. so when you turn on the car(not starting it) the light will come on. now you want to get that light to go out, and if its your 20amp fuse its something in the EFI system, thats like everything..lol
ok now where my short was, mine was in my CAS. the three wires had some how gotten melted together. so i seperated them, and had to run a new ground to inside the car, because it was all burnt out. and that was behind the center counsle down by your ECU. now you have to untape all that wiring because not only did it melt to those three wires up top, it also melted to some along the way to the CAS from inside the car.
so in short this sucks but you will get it, there is only so much wiring you can look at.
if you need anymore help hit me back