So through the process of illimination, I'm thinking I have a bad injector on my #4 cylinder. They look easy enough to change. Is there a process I should follow? Thank you!

 

I'd pull the fuel pump fuse and start the truck a couple times to help purge excess fuel from the system. Then use the schrader valve on the fuel rail to remove any excess pressure. Then remove the fuel rail. Good idea to have some extra fuel injector o-rings on hand. The o-rings are not expensive. While the fuel system is purged now would be a good time to change the fuel filter also. When finished installing everything turn the key to the "run" position and let the system build pressure and check the fuel rail/injector area for leaks.

 

Ok. Someone told me that you can unplug the reset button (for crashes) and start it and that would relieve pressure also. I already changed the fuel filter trying to solve the problem. Wish I would have relieved the pressure for that!

 

Today I changed the #4 injector. I no longer have a #4 misfire code. I still however have PO300 mil and PO300 pen codes. I know this means multi cylinder misfire but what is mil and pen mean? I have googled it and the only thing that I can figure is catalyst damage. What does that mean?