I change six spark plugs yesterday on a 4.2 three of them had carbon buildup on and four five and six had nothing what could be the problem there

 

What was the reason you decided to change them?

 

Post pictures of all plugs for diagnosis.No way to tell from a simple description.

 

Let's face it,most folks don't just decide they are going to replace spark plugs today because they don't have anything better to do.

What you have discovered is the result of something and in order to offer a worthwhile suggestion , what resulted in this situation is important to know.

It's like I have a pain in my foot why? Simple just take your shoe off , if it goes away the problem is your shoe. The real problem is a nail poking your foot, not the shoe itself.

A lot of engine problems are not always the result of the obvious, so we need to get the entire picture

You could always replace the plugs and hopefully move on,,,,,,,,,,,,,,,,,,,,,,until the problem presents itself again because replacing the plugs didn't correct the root cause.

 

Her are the plugs