Backfire and hesitation around 2500 RPM

[JeremyM]

Hoping someone may have something. Just swapped the engine in my '07 GT Auto. Idles great, fires right up, however I am getting hesitation around 2500RPM through 1st,2nd and sometimes 3rd. Once it breaks passed, it screams. From a stop to WOT it seems ok, just during normal acceleration.

Validated TPS, MAF, Injectors, Coils, and installed brand new plugs and fuel filter. Any thoughts?

 

[eighty6gt]

BAMA tune!?!

 

[JeremyM]

no tune unfortunately

 

[JeremyH]

Charge motion valves dirty/sticking?

 

[08MustangDude]

Charge motion valves dirty/sticking?

Sounds like it. They are programmed to open all the way at WOT, so when
he steps on it, they flick open. When gradual, they open gradually, may be
getting stuck.

 

[JeremyM]

Thanks for the suggestion. I'll pull the air intake manifold tonight and check everything out.

 

[JeremyM]

No dice on the charge motion valves. Pulled it all apart, cleaned the carbon build up with a wire brush and carb cleaner, reassembled and same issue. It seems to open and close cleanly. It does appear to be occurring at a lower RPM 1250-1500, but still backfires and hesitation. What's the odds that the actuator itself is bad? I can see it responding but not sure it's accurately doing so.

Also, may be an oversight on my part, but I swear it was sprung closed when I took it off. After cleaning and reassembly it was sprung open. May be nothing more than lack of attention to detail, but what is the normal position?