My car has been vibrating bad at idle since I put in my headers which was about a year ago. During accelerate the car seams to be hesitant and bucks. It doesn't accelerate anything like it did when the car was completely stock. I also get a loud boom from under the car when i accelerate hard but its usually on the in the shift from 1 to 2. By the way its an A4. I think its the tranny mount but I'm not sure. So i got under the car to check it out and noticed that my y pipe isn't even connected to my cat. Some how there is a nice dent in the exhaust bend right after the cat. Would these 2 things account for the major lose in fuel milage and power? I would think that would also be why it keeps back firing too. Also had to replace the air pipe last week cause it complete snaped in half. So not sure what happened to my car but it looks like its been through a war. Any help from you guys would be great.

 

Tranny mount is broke most likely.

If that is a severe dent, then sure it can cause serious lack of power.

If the dent does not fix your backfire issue, maybe the o2's are sending false lean conditioners because they got contaminated by the headers burning coating off or something, I dunno.

 

sorry just to clearify the cat and back part of the exhaust is totally discounted from the end of the y pipe back. Stupid shop didn't put it back together and I didn't notice til now. The dent is about the size of an apple but only pushes in maybe couple cm.

 

And you couldn't hear the sound of what was essentially an "open" exhaust?

 

yea i could hear it but me trust the mechanic and not knowing a ton on cars thought is was something else. Didn't think to look under there til today.

 

my tranny mount was bad and when the car shifted 1st to 2nd you would hear a big bang.