87 gmc jimmy ecm

i have a 1987 gmc s-15 jimmy that keeps blowing the 20 amp lower right fuse truck will start and run for 1 min than blows fuse i see no visible frayed wires could it be something else besides the ecm ????

What fuse no or label on fuse is it blowing?

it was bottom left marked ecm 1 this happend on a rainy nite i let truck sit 2 days and now it starts and runs!! thinking wire harness is letting water in?

Might check the injector wiring under air cleaner adapter.
The sometimes get shorted or pinched there.
Good Luck