Hesitation at specific RPM

[elpiar]

Hey guys I finally fixed all my IC piping and wastegate problem so I know I don't have leaks in IC piping and wastegate.

But now I notice that under WOT (15 psi setting) there is hesitation around 4200-4700 rpm. Especially in 2nd and 3rd gear. I also notice that the boost gage kind of drop to 13 psi momentarily. The AFR shows solid high 11s.

Even if there is still leak or wastegate problem, why does it occur at a specific RPM. Could this be tuning related issue?

[DevilMB3017]

It sounds like you might have a vacuum issue somewhere. This could cause your boost to drop because the wastegate is opening incorrectly, or your blowoff valve is popping, or your fuel pressure is dropping...

I'd check all your vacuum lines and make sure everything is okay.

Edited to remove stupidity.
Modified by DevilMB3017 at 6:06 PM 10/14/2008

[WDRacing]

Optimum AFR is 11.5 to 12.5 under load / boost. Having a hesitation that always happens at a certain rpm is weird, what management are you using?

[C-Kwik]

Spark blowing out?

[elpiar]

I use calum realtime ECU