I did a tune up in my 1989 Chevy Suburban 350 engine. I did the plugs, wires one at a time so that I would not get out of order. Also did cap/rotor. But now it runs terrible. Do you think I messed up the firing order somehow?
Attached is the diagram of your firing order and location on the cap.
If you still have running problems after verifying correct firing order and location, it is possible that a plug wire is not fully seated on the plug or you cracked a plug while installing.
You would also want to look around the motor for possibly knocking off a vacuum line.
These would be the most likely causes of your poor running condition now.