I have a cnt high flow cat downpipe, along with that i have an ets intake. I have been driving with the downpipe for about 3 weeks now and just recently installed the intake a week or so ago and now my car is making a strange low grumble that seems to be coming from the downpipe. To be more specific, it doesn't make the noise at idle or acceleration, only when i close the throttle and the rpms are between 2500-2000, then when i begin braking it also stops. Any theories are much appreciated!

 

My theory is...

CAVEAT: I'm assuming you're not tuned

Your ECU has gotten used to the Intake being there and started adding fuel to compensate for more air which causes your car to backfire just a little. Now that you have a high flow cat the backfiring is more pronounced.

If you're tuned I guess that still applies but I don't think it would be as pronounced. Point is when you replace restrictive exhaust components like cats, and mufflers you hear more sounds including backfiring etc.

EDIT: To be on the safe side if you can make sure you haven't developed an exhaust leak on the part you replaced that could also add some unwanted noise.

 

Are you using any engine management? Ecuflash, AP or Protuned?

 

Thanks for the reply and you are correct in the fact I'm not tuned yet, I was going to wait a month until I got intercooler pipeing and then get it pro tuned, this shouldn't cause any issues should it? Thanks again!

 

Are you at least flashing it with a cobb ap or ecuflash software? Please don't tell me you slapped on an intake and a turbo back without a tune....if so don't drive the car until she's tuned, terrible idea.

 

Ya, i have an AP but i just feel like a protune will pull out some more power. I actually replaced the gasket and it seems much better now, thanks for the help! I am also just being a bit overly paranoid because this is my frist really nice car and i dont want to break it lol. Thanks again!

 

In that case I'm definitely sure that's backfire from fueling. I read that Cobb's OTS tunes work with more fuel and less boost to keep detonation at bay plus add the fact you got a less restrictive exhaust and voila` you got a nice soundtrack.

Where in TX btw?

 

Mckinney! (so just a bit north of dallas) ya, im much less woried now cus I've have a few others tell me its fine, I'm just cautious!