hello, I have a 2010 silverado with a 5.3 V8 and recently while driving I got a service stabilitrak, service traction control, and a rough idle while also drives with high RPMS. I took the truck home and the code reader read P0304 for cylinder 4 so when I youtubed it the first result was to change the spark plugs. Mine were changed last year so I only changed the spark plug for cylinder 4. That did not work so then I also changed the ignition coil and started it up and nothing changed. I then noticed I smelled fuel so my suspicions went to the fuel injector. I changed 1 fuel injector (the one for cylinder 4). And nothing changed. Frustrated now I don’t know what to do. Any help or advice is appreciated. Also I no longer smell fuel so I think that injector was bad but I’m not sure. Thanks

 

I had this exact set of symptoms and code 4 years ago on my 2007 Silverado 1500 .
I replaced my plug , no change . I swapped coils with a different cylinder , The miss remained on #4 . I did not do a compression test that I am going to recommend you do .
I felt a definite pulsation in the exhaust at the tail pipe .
After searching You Tube videos I removed the Passenger ( Right ) side rocker cover .
And could see that #4 Intake rocker was not moving like all the rest of the rockers .
At this point I began looking into replacing the lifters which entails removal of the cylinder head to do . Then evaluated my options based on that engine having nearly 200,000 miles on it and Costs of Rebuilding locally to MY Standard or Replacing with a Remanufactured Long Block with a warranty .
I chose the Reman engine option due to costs and the fact it came with a warranty (and choices of warranty coverage )
I ordered Mine from Powertrain Companies because they had the best options and had units already done and In Stock ready to ship .
My New engine has not skipped a beat in the last 4 years .
So it’s pretty much your choice from here on out .
I recommend doing a compression test on all 8 cylinders and Pulling the passenger side rocker cover to visually observe the actual movement of the #4 Cylinder rocker arms because your code is for cylinder 4 second from the front on the passenger side .
I can refer you to a salesman if you decide to go that route . And They offer a 10% discount for Veterans .