Magnaflow with A/T issues

[misk]

So I recently installed a Magnaflow Cat-back system on the 1 and really love how deep it sounds under 3k RPM. One thing I have noticed while driving in steptronic mode is that when you down shift the car still accelerates with foot off the pedal. With the stock exhaust it would decelerate immediately. Does the change in flow from the cat back system confuse the ECU and gear ratios? Has anyone had this problem before?

Also worth noting is that up shifting in manual mode the car almost feels like its double clutching with gears upward the RPM remains the same but load on the engine is higher. (you can hear it)

Any feedback would be great.

[AW128i]

I'd say what you're feeling is normal. Perhaps you didn't notice it before the exhaust because you weren't paying as much attention to it? With the downshifting, I've noticed that the ECU will sort of rev-match in Steptronic mode. I think it's that, that causes a sort of freewheeling feeling, which can be mistaken for accelerating. It's not that the car is accelerating, it's just coasting briefly when you're expecting perhaps deceleration.

As for the upshifting, this is still a torque converter automatic so perhaps you're noticing the brief period of time when the transmission has upshifted but the torque converter is in the process of locking up (the TC is unlocked in-between shifts)? Maybe not, since that is a split-second thing.

Overall, you're probably more aware of what's going on because the engine load is now more distinguishable since the exhaust is enhancing the volume and tone of the engine.

[Greenkirby21]

Originally Posted by misk

So I recently installed a Magnaflow Cat-back system on the 1 and really love how deep it sounds under 3k RPM. One thing I have noticed while driving in steptronic mode is that when you down shift the car still accelerates with foot off the pedal. With the stock exhaust it would decelerate immediately. Does the change in flow from the cat back system confuse the ECU and gear ratios? Has anyone had this problem before?

Also worth noting is that up shifting in manual mode the car almost feels like its double clutching with gears upward the RPM remains the same but load on the engine is higher. (you can hear it)

Any feedback would be great.

I think its because the steptronic is slow to downshift. At least for me, downshifting is horrible. It takes a good two seconds for it to downshift.

Secondly, I think the car is actually holding the exhaust better when upshifting. It might be my intake, but when shifting at the sweet spots(~3k) then it doesn't feel like I am losing much power as before.

Since these are just bolt ons, it shouldn't affect anything drastically.

If I were you, I would try resetting your auto transmission, since the car over time learns your driving style. Also, give it some time for the ECU to adapt : )

[misk]

Thanks for the info guys. Yeah I guess I will give it some time to just get used to everything and maybe reset it down the road.