backfire on 1-2 shift wtf?

[OrangeMustangGt]

ok guys i know my car needs a tune bad, and this may be the problem, but when i do a high load/rpm shift from 1-2(assuming i can catch2nd), i get quite a loud backfire out of the tail pipes....wtf? what could cause this, it seems to happined recently, but ive been messing with my fp again...

 

[4Jenna]

Lean condition can casue that

 

[Hydrocarbon]

Sounds like your computer is pulling fuel when you let off the accelerator to shift, causing a lean condition.

Maybe increasing fuel pressure 1 psi might help?
Also if your bored you might want to verify some of the sensor outputs. Like the ECT and the ACT sensors. Just to make sure they're sending the computer the right info...

 

[Darkhorse845]

Lean condition can casue that

Thats the same
thing I was thinking.