I have an AEM CAI and the person before me deleted the secondary cat and welded (very poorly) a 3" home-made exhaust to it.
I tuned with Steve at E-Tunez with my FlashPro and was very satisfied with the result.
I recently ordered and installed my Fullrace Catless downpipe and Yonaka 3" exhaust.
It sounds much less raspy, and power has increased.
I do get that hiss when I go anywhere above 1/3 throttle, like most catless downpipes.
However, when I sent Steve my first datalog after install, he replied with the following:
"These logs indicate an oxygen leak on the PO2 sensor, or the sensor itself is not fully installed properly. Check the exhaust for leaks at all junctions and at the head. If I adjust based on these values the car will lose a fair bit of power. It looks like the MPG is way down based on what I can see."
I confirmed that the bolts where the downpipe meets the engine are tight.
I confirmed that the bolts where the downpipe meets the midpipe are tight.
I reused the stock gasket. Does it need to be positioned a certain way?
I did not unclip the O2 sensor when I uninstalled/reinstalled it, since I felt there was enough slack in the wires, is it possible that the wire was damaged?
I left the "cup" on the primary O2 sensor, since there was no intuitive way to take it off, could that be creating a gap?
The O2 sensor didn't drop, hit, or otherwise become damaged.
ANY help is so much appreciated.