Apex'i Downpipe Problems

[19GS-t97]

Ok i have my boost in my car set at 15psi. I had a stock downpipe on it with the apex'i n1 cat back and it ran great throughout the rpm range. After i installed my apex'i n1 downpipe, when the boost gets around 12-13psi the car starts to studder and almost feels like fuel cut. The car had a coolant problem so i took it to a shop where the owner said that the computer recognizes that i have the boost too high for it and it wants to cut it back down which is the reason for the studder problem. Does anyone have any experience with this or know if he's right or wrong? Any suggestions would be great

Thanks

[chico904]

it's seems to be the universal answer.. but boost leak test.

[sureshot971]

definetly boost leak test, I dont see how a simple downpipe could cause something like fuel cut unless you turned the psi way up. I had a n1 catback with stock dp, and then later upgraded jsut like you and had no problems at all.

[19GS-t97]

ok under part throttle boost when it gets to around 13psi it stills studders a little bit, but under full throttle conditions there is no studdering...There was a boost leak around the throttle body elbow but i re- tightened everything. No more boost leaks but still have this problem. Could it be caused from not having a cat-converter any more by any chance? also does anyone know about the ecu recognizing the boost being too high or was the mechanic just talking out of his a**?

Thanks

[19GS-t97]

set of plugs did the trick