I have a 89 4.0 cherokee. and a month ago my jeep started knocking. I took the valve cover off all the springs and rocker arms seem to be fine. I put some stuff in it to help raises lifters because dad thought it was my lifters. But It still knocks and it only knocks in high rpm's and when im in park. Help annyone??

 

How's your oil pressure?

 

Have you used any cleaners like seafoam? Carbon build up in the combustion chamber can cause knocks. Also, have you changed and properly gapped the plugs?

 

Your jeep is a renix. It has knock sensors. I would look into checking those.