Howdy everyone, I have a 2001 Expedition 4.6L XLT, rwd, 186K miles. A few weeks ago, while driving, I heard a thump toward the front of the vehicle, then the knocking started. It is a definite metallic knock which only occurs above 1500RPMs while accelerating. I was doing ~20-30mph at the time. When I let off the accelerator, the knock went away. The truck did not throw a code until I got home, then it was P0301. So, I opened her up, and replaced the #1 plug and COP. [I bought a full set of plugs and COPs a few years ago, and had leftovers.] The knock persisted. Next, I replaced the #1 fuel injector with a new one. The knock persisted. Not only does the knock return whenever I accelerate, but after a few minutes the P0301 returns too. To clarify, it is definitely a p0301 and not a p0300. I've replaced all the components there, and don't know what else to do. This is my daily driver. I'm a decent shade-tree mechanic, but this is straying outside of the things I know how to do. Any advice would be appreciated. TLDR; Truck : 2001 Expy 4.2L 186K Knocking on passenger side of motor Symptoms : The knock can't be heard while the engine is idle, only on acceleration over 1500RPMs. Low speed acceleration - Knocking Coasting regardless of speed - No Knocking Unsuccessful attempts to fix the P0301/Knock: -Replaced plug -Replaced COP -Replaced Fuel Injector -Fresh Oil/Filter change.