Breaking up! Need advice

Ok car was fine running and driving great. Without any problems. Just changed oil, filter, spark plugs etc. Car had a straight pipe 3 in no cat or muffler from turbo back. So I bought a vibrant turbo muffler 3in single tip. Bought for 30$$ uses but good condition" that's $190. Muffler" so I got it installed today. And now the car is breaking up at about 4-4,500 rpms at about psi
Car has stock Ecu
Small 16g
Stock injectors
255 walboro
Fmic
/ubbthreads/images/graemlins/dunno.gif I don't have a clue y it's doing it now out of no where. Just started doing it today. I'll work on it on the weekend as I have more time. But if anyone has any ideas. I'm open to all ideas or at least where to start.
Thank you

 

[James]

Check the basic first?

Boost leaks
Plugs
Wires
Coil pack
Transistor


My car will SOMETIMES get a bug and sputters/breaks up badly around 5k. I can't figure it out for the life of me. If I turn the car off and turn it back on the problem goes away till whenever. I've check everything except fuel pressure but in not leaning out. New Wally is on the way so ill see what happens.

 

[5OF2k]

As above, check the basics.

You also need injectors with that setup, FWIW.

What heat range ug are you using, what gap, what type of plug wires, and what boost are you at?

-Jake

 

[Jason G.]

Spark plug wires