2006 engine knocking noise when cold ONLY
I have a 2006 F150 4.2 V6...when truck starts after sitting 4+hrs(cold) it knocks, sounds like a lifter noise. Replaced all lifters, checked pushrods for bends or damage...After motor warms up noise goes away. I can change oil then start right way NO noise. only if engine is cold does it make noise...Could it be oil pump or pressure release valve?? can pressure release valve be changed without removing timing cover??
Thanks in advance