I bought an MBRP Cat back exhaust and had it installed on my 07 4dr JK by a reputable muffler shop. They tack welded it together and off I went. The damn thing sounds phenomenal and I can notice improved throttle response. However, I am having a, what I hope is, a small problem. As I am driving, when I first tap the brakes to slow down, the engine revs from 800 rpm up to 1200 rpm. It is just a blip as it comes right back down to 800. Then it does the same thing when I come to a complete stop and then it goes back to idling smoothly. I am also running a Brute Force CAI. It was not doing this prior to the cat back install.

Any ideas?

 

You may be on to something else. But I'll guess with my I am guessing that as you are slowing down the transmission is downshifting and you are noticing the motor rev (a little more) becuase now you can hear the exhaust, and once again when you come to a complete stop. Just a guess, but I am pretty sure mine does this as well.

 

x2 on downshifting. best way to know if its something out of the ordinary is to have someone come with you like a mechanic or video tape it and post it!

 

As far as the sound goes, I may be hearing the downshifting for the first time because of the cat back, but I have never had the Tach jump from 800 to 1200 RPM and back down again.

 

Had my MBPR Black cat back's installed by my Chrysler Jeep dealer and they are sounding and working just fine. My 2010 Wrangler Sport is a 6 speed manual. Is yours manual or automatic? I don't notice any abnormalities in my Tach except for what is normal when downshifting.

 

It is an automatic.

 

My auto does the same thing. Before and after I modded my exhaust, I've had it happen with all the V6 chrysler vehicles I own. Usually happens when auto shifts down from 3 -2 or 2-1. The down shift has a much more noticeable sound, kind of a light pop and gurgle down to ~800-1000RPM

 

For what it's worth I have a similar thing happen to me. It almost feels like when I used to down shift with a manual to help slow the car down. I haven't looked at the RPM's but I do feel the transmission down shift during slow down more since I put in my CAI and exhaust.

 

my question would be, what did they weld? i thought this system was a bolt on?

 

They tack welded the system instead of bolting it in. (pipe joints).