My neighbor has a 98 6.5 "F". He came crying to me the other day that his truck did NOT pass emissions...In fact it failed miserably. I was stumped. Last night he came over and said it finally passed. When I asked what the problem was...he said that he was running a new K&N filter when he failed...after installing a new stock filter and putting the box back on, he passed with flying colors. Does this make sence. He said the dealer told him the truck will produce more h.p. with a stock filter in the box than an exposed K&N. This is the only mod he has.Now I am really stumped. Should I go back to stock filter even though I am getting ready to install my 4" exhaust:help2: ?

Your comparing two different things it sounds like. "exposed" K&N compared to factory filter in the factory box. Why didn't he just get the K&N replacement element that would fit in his factory box?

Personally, I don't think the 'new' K&N filter was his problem.

guybb, here's the rest....