Why would this happen after replacing fuel injectors?

Question

I changed the fuel injectors properly. No short cuts and now this code tripped and it runs horrible. Its smoking now. It smells like its burning old carbon off the pistons. Spark plugs were done at the end of october

Answer 1

The fuel injector seat that seat in the intake  manifold is that properly sealing? If you have brake cleaner or carburetor cleaner spray that area, and note any change in idle ,