I have 96 silverado 1500 5.0 4x4. I did a tune up..plugs, wires, cap, rotor, air filter... when I put everthing back together and started the truck. The CEL came on and I noticed I forgot to plug the sensor plugs for the air filter back in, when I pluged them in the light went away. After a day or two the CEL started to blink (P0301)..It has been mifiring ever since in cyl#1. Did a compression test and all was fine in that respect. I changed the fuel filter and re-replaced the cap and rotor just in case it was bad, no change. Also since it started I can here what seems to be tissing sound, maybe an exhaust leak? Im stumped! We did do one other thing because I have spark in all plugs we pinched the fuel return line closed about half way, when we did this the misfire went away. Any ideas would be awesome..

 

Move the plug to another cylinder and see if the code follows it if not could be a bad wire or injector