Engine KNock tick after spark plug began to fail/after spark plug change.
 

A few weeks ago I noticed a slight shudder in my2005 f-150 truck when idling at a stop sign or light. A few days later I hooked it up to a diagnostic tool and it read that there was a rich fuel mixture in cylinder 8. The truck is over 80,000 miles, so I assumed it must be a spark plug issue. Knowing the unbearable nightmare that is the Triton 5.4 I ran a cycle of carb cleaner through her in preparation for changing the spark plugs to clean the injectors and hopefully loosen the carbon around the plugs. I put another does in the next week when I topped up. I had to wait for payday to get plugs, anti-seize and other required tools. The day that I got the parts I started experiencing a tick/knocking sound from what sounds like the driver side. I stopped driving it immediately and parked it at my house. After replacing the plugs I got everything put back together and started the engine, I immediately noticed that I the ticking/knocking sound is still present. I am hesitant to drive her to see if the shudder is still present, I used a torque wrench to tighten the plugs down to 25 foot lbs, but I've heard some say that with the antiseize it needs to be higher. I did not replace the coils or wires due to funds, and I've heard this as an issue. I'm hoping someone who has more experience working on the Triton can point me in the right direction.

You may have a problem that was misdiagnosed !
What was the code for # 8 cylinder?
You may wind up removing the valve cover and check out the valve springs for #8 cyl.