I've been following the SC forum for awhile and have gotten lots of great info! Any help on my problem would be greatly appreciated. A couple of weeks ago I installed a Kenne Bell on my 2001 4.6L auto F150. With light throttle conditions around 2,000 rpm it has a stumble and some hesitaion. The stumble is most noticeable on takeoffs and low mph in 2nd. Occasionaly in 3rd and 4th I can detect faint detonation. Fuel pressure doesn't drop off and the problem only develops after the engine has reached operating temps. Problem gets worse when outside temps drop. I've tried various 91 octane fuels.WOT is problem free! Kenne Bell told me it was a vacuum leak, but have yet to find one. It's a minor but annoying problem!

I didn't have this problem with my powerdyne. But a slightly rougher idle did develope with my pdyne.

I believe Crash and or Skidmark(correct me if I'm wrong) installed a KB not too long ago. If you guys can help me that would be great. In fact any input would help.

 

JSC, it's quite possibe that it is a vacuum leak. I suggest you check all the lines again. Also, if you are detonating, the timing and A/F on the KB chip might be incorrect. KB's are supposed to run optimally with 92+ octane. Heck, there was even an octane warning sticker on my KB when I received the kit.
I've since done numerous modifications, but I'm a speed freak too.
One suggestion might be to have a different chip put in tuned by a proficient tuner. That should clear up problems. The stock KB chip is relatively conservatively programmed.