Not sure what happened to my last post. I can't seem to find it anywhere. Anyway, I have a 2000 F-150 4.2L I'm working on that runs very rough and shakes. The entire passenger side of the engine is throwing missfire codes and the exhaust manifold on that side remains cool to the touch after a minute or two of running. All the spark plugs are getting spark. I took the valve cover off and discovered that the valve at the very back has a mangled spring. Would just one broken valve spring cause that entire side of the engine to missfire? Thanks!

 

Can you list all codes? The cylinder with the broken valve spring should not affect the other cylinders. How did you verify that spark is present? If you are sure there is spark present at each spark plug, the injectors for the affected cylinders may not be working. Are the plugs wet with fuel? Done a compression test?