Hello I'm new to this forum. I'm having an issue with an expedition I own. I'm a ford guy but this expedition is changing my mind. I finally took it to a shop after I got done throwing parts at it and they said it has low compression in cylinder 8. Sure I believe that but they quit diagnosing all the issues I wanted looked at after that. It idles rough and runs rough at low rpms and just started knocking. I realize it's needs a motor or a rebuild I can live with that what I'm dying to know is what caused that to happen is it the timing chain or a camshaft issue or could the exhaust be plugged converter or manifold...? Also it did rattle in the driver side towards the back when you gassed it but that stopped

 

The #8 cylinder needs to be borescoped. Also, pull the valve cover and make sure the cam and followers are okay for that cylinder.