When cruising down the highway at 70ish mph and occationally while cruising down the road, I hear a popping sound coming from below the car in the area where the cat and mid pipe would be.

I know that some folks were having an issue with the cat since it didn't have a hanger like the stock piece, but I can't tell if what I am hearing is the cat hitting something (likely the underbraces) or possibly mini backfiring due to the engine running lean at cruising speeds. From the passenger seat, it sounds like its coming from up near the engine, even though the stock cat hanger was in the rear.

just wondered what other folks with the cat hear or feel. I have the stock exhaust.

 

does it happen when you're letting off the gas?

how about if you rev it really hard?

 

Hey Brillo, they are two very different sounds. The cat hitting against something, you'd definitely know. Just in case, have someone rev the car up, and lay down next to the side and listen to it. I'd suspect that what you are hearing is just the cat backfiring.

 

i heard it most clearly when we were cruising at a steady speed on the highway going up and down hills, not when i let off the gas

 

back out.

that popcorn popping sound is detonation.. the location you give is exact... back of the cruise afr..


beers

 

pm or call me this is serious!!!!!!

beers

 

I pulled the interceptor to be safe and switched back to stock. No issues or noise. I still think I here the cat hitting something on bumps.

Its weird, we tested the lean afrs for cruising on a dyno, and we had worked the car over pretty good by that point, i wouldn't think 15.2-15.5ish would be that bad. Well, I'm going to re evaluate my strategy as far as cruising maps go.

 

Brillo - have you read what RB has to say about tuning for fuel consumption ? Its in the Tech info for the flash tune.

Worth a read

 

I did, but I figured were working mostly inside the cat temp/emissions box, therefore I thought I'd see what else i could eak out emissions be damned.

it turning out to be harder than I thought, but i'm not totally out of ideas yet.

 

Did you solve this problem yet?

 

Well, I had thought it might be knocking, but since I didn't experience any loss of power and i still hear the noises with the stock ECU and premix, it has to be the cat rattling or hitting something. It takes a while for the sound to develope, but what I think is happening is that the rubber hangers eventually heat soak and the fact that I'm one hanger short causes them to flex mroe than they should.

I was worried I was hearing the same thing as Swoope, but we discussed the issue and I'm pretty sure that it is the cat, as the sounds I hear were only after the cat was installed.
I'm going to get a hanger installed this week to help hold it in place.

 

Well, I had thought it might be knocking, but since I didn't experience any loss of power and i still hear the noises with the stock ECU and premix, it has to be the cat rattling or hitting something. It takes a while for the sound to develope, but what I think is happening is that the rubber hangers eventually heat soak and the fact that I'm one hanger short causes them to flex mroe than they should.

I was worried I was hearing the same thing as Swoope, but we discussed the issue and I'm pretty sure that it is the cat, as the sounds I hear were only after the cat was installed.

I'm going to get a hanger installed this week to help hold it in place.

 

Maybe it depends on the exhaust its matched up with, or the version of the RP cat, because I had an earlier version matched with the RB exhaust for about 8 months, and never heard any rattling. But when I was helping IzoomzoomI put a Supercat on his Helix, it made a horrible rattling sound, even at idle.