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There is no cat in the catback exhaust. Only resonator and mufflers.

I installed my Cobb Catback this weekend and although it did not eliminate the stumble, it is now less harsh. Still there, but no longer a fall on the face.

The only differences I saw were the 3” Piping back to the Y and a shorter resonator.

So, I was previously on Cobb Downpipe and protune with no noticeable stumble. Added the UEL Header, Intake and supporting fuel mods plus a couple other pieces with a new tune and that is when the stumble showed up.

Car is back with the tuner today and hopefully he can work the rest out.
 

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Added the UEL Header, Intake and supporting fuel mods plus a couple other pieces with a new tune and that is when the stumble showed up.

Car is back with the tuner today and hopefully he can work the rest out.
Did you mean Equal Length Header? Also, what's your verdict with your revised tune?
 

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Did you mean Equal Length Header? Also, what's your verdict with your revised tune?
Sorry, yes. Equal Length Header.

To be honest, I installed a Cobb Catback system before I brought car back and it smoothed out the stumble quite a bit. The new tune focused on dip in settings, but he could not eliminate the stumble. He claims he saw the stumble while on the dyno tuning and it was asking for 8% fuel add. He’d add the 8% and then on the next test, it would ask for 8% again and make no difference. He believes it mechanical and can’t be tuned out.

The revised tune felt better overall, but as before, the more I drive it, the less linear it gets. Is the ECU trim learning causing this? If I reflash the tune and clear and start fresh, it will go back to feeling cleaner and then just gets worse again.

I’m going to try and get through multiple tanks of gas and see how things settle in.

I have talked to other tuners about this and they feel like I shouldn’t need the whole fuel kit with rails and lines, so I’m not going to jump in and spend another $1000 plus to find out right now.

I have scheduled time with another tuner and see what can be done, as I’ve only worked with this one tuner on the Subaru platform.
 
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