I bought an 05 FX4 Screw about 6 weeks ago with 54k. Came with a Flowmaster, K&N filter, and a throttle body spacer. I can't tell over the exhaust if the engine is knocking or not. Was driving close to buildings, to try to hear what I think maybe knocking at crawling speeds, when lightly accelerating... using 87 octane... Don't think the previous owner had the chipped reprogrammed, but not sure.... Any suggestions ? ? ?

 

Alot of the 5.4's have loud fuel injectors.

 

with those bolt on mods, you think i should bump up the octane ? ?

 

Could also be the cam phasers.

Get rid of the throttle body spacer, by the way. It does nothing for you except cause noise.