I have had installed a AEM Brute Force intake on my 2002 5.4. I was recently helping my friend purchase a CAI for his 06 5.4, in my research I learned that anything bigger than a 3" would cause lean issues without a programmer on the 04-08 trucks.
I was wondering if this would cause any problems with mine so I measured and discovered mine was a 4" system? Are there any downsides to having one this large and am I in danger of running lean? I do not run a programer nor an aftermarket exhaust (although both of these items are on the wish list).
-Tanner

 

Does their website or the install instructiions state that you need a custom tune? You can contact AEM and they should be able to tell you.