I have a 96 GMC 5.7 vortec that keeps blowing ECM-B 20amp fuses the truck will just quit and then if you let it cool down for about an hour it will let you put in a new fuse without it blowing and run for about another hour. Heres what ive done- I replaced the fuse with a fliptop off a beer can and that got me off the highway( I noticed when i did that the fuel guage pegged past full), i tried a 30 amp and it blew with just the ignition on, i replaced the fuel pump relay and that did nothing, i played with the wires and havent found a short anywhere on the top side. Any ideas whats going on?? by the way if i get it running and just let it sit and idle it will still blow the fuse. The fuel pump isnt that old could it be the pump wiring??

 

Have you had any tranny work done lately? If so inspect the harness over the trans that supplies the o2 sensors for a short. Have had 3 customers in last 2 years with same problem.