ecm fuse blowing

My son has a 1991 chevy k1500 yesterday the truck died as he was driving the ecm ign fuse was blown put new one in and it started today did the same thing after replacing the fuse 4 times finally ran only does it when in the run position driving down the road any help would br great thanks

For what it's worth, I'll tell you what the ECM/IGN fuse powers on an '88. Your '91 may be different and probably is.

1. ECM
2. Stop/TCC Switch
3. EGR
4. ESC (Electronic Spark Control)
5. EVRV (Not sure what that is but maybe evap system)
6. Air Switch (Not sure on this either but maybe the air injection smog pump).

The ignition switch powers this fuse plus 2 others so I don't think it's the wiring from it. It has to be something downstream from the fuse that's shorting out and that can include a chaffed wire shorting to ground. Hope this helps and remember this is an '88 manual I'm looking at..............Steve

had a wierd deal with my 92. ECM fuse popped for now apparent reason. Could not find the short. Finally found were the air cleaner had rubbed the wires that feed the injectors and ground was there. Had to replace the pigtails at the injectors. THe design of the air cleaner allows the wires to get pinched. If you don't see something else...make sure you are ok on this.