open cutout vs full exhaust question

[Reaper6]

my car seems to misfire and run richer with the cutout open. But if i close it it runs fine and seems to have no problems at all.

 

[ChrisTR]

Does the boost creep a little higher when the cutout is open maybe?

 

[streetknight]

Hmm, should lean out with the cut out open. Have any scan tool data?

 

[Reaper6]

O2 readings were all over the place, it happens when im just cruising the car. More around 1200-1700 rpms.