I am the new owner of this vehicle for 2 weeks, and my mileage was 12.5 mpg average. I replaced my spark plugs yesterday with motorcraft plugs on my 09 FX4 5.4l. The process was a breeze, one of the easiest plug replacements that I have performed. The truck has 84,xxx miles. After the plug replacement, and approx 40 mile drive, my avg mpg is 15. However, not noticeable before the plug replacement, now the "5.4 tick" can be heard. My question: should I have replaced the coil on plug assembly as well? What are the odds that the "tick" is caused by the cool pack?

 

No, those shouldn't be related at all. If it is indeed the same tick that everyone talks about on here, it is the exhaust manifolds that are making that noise. Either a cracked bolt or cracked manifold itself causing a leak. I have developed a more noticeable one myself in my 12' with the 6.2 at 71k miles. I guess Longtubes have added them self to the mod list!! Haha