Last night while surfing the internet on different spark plugs, I came cross a spark plug that is typically used in motorcycles and marine motors. It has a shorter thread than regular car plug. So I went to a local
auto store today and got a NGK (4322) BR8HS plug. Put it in the #4 cylinder and it works. Now the #4 cylinder fires well and I get much more power with all 8 cylinders working. So now, I am happy that a very simple solution fixes a big problem.
Attached picture shows the shorter NGK plug and a regular plug.