Ok, here is the background. I have a 2004 F-150 4.6l with an aftermarket grill, K&N Filter and a custom 2.25" cat-back with dual flowmasters (those are the only related add-ons).

Over the past few months I have been noticing a hesitation or bucking of the pedal when making the first few turns out of my community. It feels like I am pumping the pedal. Also, the A/C was also not blowing cold anymore. I took it to the Dealer and they said Oh, the A/C is because of your grill and the hesitation/bucking is due to the exhaust and filter.

I did not agree and took it to another shop for the A/C issue. He tested it with some gauges and said it is low 2lbs and there is probably a leak. I took it back to Ford and this time they found out that the AC Accumulator needed to be replaced and they did so. BUT, they are still claiming that the exhaust and filter are causing a lack of back-pressure that is causing the hesitation/pulsing. Is that also total crap?!

I busted them on the A/C lie, and I think they are not even checking the truck and just blaming the aftermarket parts! What is your advice?!?!

 

They're blaming the aftermarket parts, take it to another dealer. The aftermarket grille couldn't affect the a/c, because it pulls air in from by the wipers or in the cab on max a/c.

 

I don't know if this helps but I have a 2003 F150 with V8 4.6L and dual flow masters. I have not had the bucking pedal problem that you are talking about. Sorry, but I can not help much more than that.

bman59