Engine is making a knocking noise after driving it. Engine is fine when driving until it comes to idle speed at a stoplight or when going to park or back up. One mechanic checked can phasers and indicated all were "ok". However, tension chain becomes loose when idle stated by another mechanic. Question is why is this happening?? How should repair? What about tensioners need replaced etc or what? Need help.

 

What year and what engine? Perhaps listed in wrong section, the 4.9 or the 4.2 don't have cam phasers.

 

Sorry, 2008 yr. f150 mechanic thinks oil pump is problem. Installing new one today. We will see. Hope it cures oil pressure problem and knocking noise.