GMC Repair: 1997 GMC Sierra C1500, 2WD 5.7L V8; ENG-1 fuse blows, camshaft position sensor, o2 sensors

Question
On my GMC with 186,xxx miles, the ENG-1 fuse blows in the Fuse/Relay Center under the hood. I keep replacing it, but as soon as I turn on the ignition it blows again. The SES light is on with P0102- MAF sensor low input and P0340- Camshaft Position Sensor Malfunction. I have replaced the CAM sensor, and swapped the MAF sensor with one off my 1999 Chevy Suburban 2WD 5.7L that has no codes nor SES light and the Sierra still has an intermittent misfire as if it is cutting out for a second and then it smooths out. Vice versa, I put the MAF sensor off the Sierra on the Suburban and it still runs fine so the Sierra's MAF sensor is fine, apparently. I am thinking that the blown fuse is what is causing the SES light to come on because if I am correct, that fuse sends power to the various sensors on the truck. And with it blown, is isn't allowing the sensor to works causing the truck to drive funny. I have done a complete tune-up and replaced the air/fuel filters as well. When I first bought the truck, the only two codes I pulled were the Bank 1 and Bank 3, 02 sensor codes. I was told it had sat in the previous owners yard for several months before I bought it, so I was advised by Auto Zone to put some fuel system cleaner in with the gas. when I added it, the SES light would go away, but after a week or so it would come back on until I put more gas and additive in it. And I just put some in it 3 days ago when I replaced the plug/wires, so it isn't reading any 02 sensor codes as of right now, but it may once this additive goes thru and runs out.  What would cause this fuse to blow as soon as the ignition turns on? Possibly, a short, or could it be due to the bad 02 sensors?...

Answer
Hi
That fuse protects all 4 o2 sensors, the cam sensor, MAF sensor, EVAP purge valve and EVAP vent valve (and if equipped the A.I.R. relay). If it blows that fast, I would unplug each item, one at a time turn on the ignition, and see which load is blowing the fuse. You'll only need 8 fuses at the most.