Magnaflow, cat back problems

[crazyfireman]

Hey everyone I have a 2010 6.2L with a 6 speed auto tranny. I installed the muffler delete Magnaflow cat back kit and am having a problem. At low RPMs the exhaust tone is changing and it sounds bad when it does it. It acts like it is missing and I am aware of the fuel management system where it shuts down cylinders but this change in tone is sporadic and I would think the fuel management would only be in the upper gears and at highway speeds. My local dealership is pathetic and they said there is nothing wrong and I need some opinions...

[norcalwheelman]

It's the AFM, my L99 A6 does the same thing at low speeds. It is annoying to say the least. Your exhaust just makes the sound of the AFM more noticeable since the Magnaflow catback removes the mid resonator. This is why I am going with an axle back setup, from what I have been reading the cat back offers no increase in HP or torque.

[ttss]

I have the MF 3 inch cat and it does the same. It actually sounds worse at low speed and rpm with a light load than highway speeds. I dyno'd the car before and after the cat install and picked up a min of 8 hp and an avg. of 10. I had already installed a CAI previously but did not dyno before installing it.

[ffrcobra_65]

There are a lot of information on here about the SS auto tranny and cat backs. It is just something you'll have to deal with or get the AFM tuned out.

[crazyfireman]

OK I appreciate the info

[camaross14]

i had a 08 silverado with the AFM and it would tell you when it went to 4cy mode ...as sson as u hit the break to slow down it cuts it back

[SGOS252382]

A lot of L99 owners are finding out about AFM the hard way. Any aftermarket exhaust (especially muffler delete setups) are going to cause an increase in
AFM noise. The more aggressive the setup the worse its going to be.

It's most noticable around 1800 rpms while cruising. You'll hear the AFM kick in and a change in exhaust note (along with a drone/buzzing sound in some cases).

1. Put the stock mufflers back on the car (but who wants them?)
2. Get the AFM turned off (requires tuning).
3. Live with the noise

[Missile Man]

Originally Posted by norcalwheelman

It's the AFM, my L99 A6 does the same thing at low speeds. It is annoying to say the least. Your exhaust just makes the sound of the AFM more noticeable since the Magnaflow catback removes the mid resonator. This is why I am going with an axle back setup, from what I have been reading the cat back offers no increase in HP or torque.

I have the SLP LM II axle-back. I get the pitch and vibration change when in the higher gears at any speed. Using the tap shift helps by driving at higher revs. I plan on getting AFM tuned out.