Kind of strange sound, actually. It sounds internal, and I checked all of my bolts from the down-pipe to the muffy. You can hear it with the car off when you wiggle the cat back and forth. It's at it's worst during start-up, and at about 2-4k RPM

Any ideas what this might be? I've got a custom catback set-up coming off of headers. Installed the exhaust about 4 months ago, and just passed emissions testing a few weeks back with flying colors.

 

Any CEL? Sounds like a piece of the internal honeycomb of the cat broke off and is rattling around.

 

<div class='quotetop'>QUOTE (hamhead)</div><div class='quotemain'>Any CEL? Sounds like a piece of the internal honeycomb of the cat broke off and is rattling around.</div>


that's kind of what i was thinking too..... but don't understand how really. maybe temperature variation?

no CEL was flipped. everything else is cool.

 

If there's no CEL, then its still filtering as it should, or enough to keep the ECU's emmision standards happy, I bet its annoying though.

How long ago did you buy the cat? They go bad from running extremely rich or high exhaust gas temp in most instances. But that shouldn't be a factor if you just bought it unless it was used before or really badly designed.

 

<div class='quotetop'>QUOTE (hamhead)</div><div class='quotemain'>If there's no CEL, then its still filtering as it should, or enough to keep the ECU's emmision standards happy, I bet its annoying though.

How long ago did you buy the cat? They go bad from running extremely rich or high exhaust gas temp in most instances. But that shouldn't be a factor if you just bought it unless it was used before or really badly designed.</div>


it hasn't even been on the car for more than 4 months. and if my ratios were off, don't you think my numbers at the emissions test would have been off? everything was perfectly normal.

and hell yeah it's annoying. haha

 

If you were running really rich (high RPM, or high-throttle low RPM) the exhaust would have much more unburnt fuel which would clog the cat, and pressure would have just worn it down more so than normal.

Since your cat is probably welded, you can't really get the loose piece out, unless you tipped the car up on rear bumper or something LOL. If its hella annoying, I would get it replaced. If you can live with it, don't about the 50-60 bucks for a new one until the cat completelyl dies and it throws a CEL.

 

<div class='quotetop'>QUOTE (hamhead)</div><div class='quotemain'>If you were running really rich (high RPM, or high-throttle low RPM) the exhaust would have much more unburnt fuel which would clog the cat, and pressure would have just worn it down more so than normal.

Since your cat is probably welded, you can't really get the loose piece out, unless you tipped the car up on rear bumper or something LOL. If its hella annoying, I would get it replaced. If you can live with it, don't about the 50-60 bucks for a new one until the cat completelyl dies and it throws a CEL.</div>

well at least i can get some comfort about it now, if it's not ruining anything.

thanks a lot man. 8^)

i'll take it back to the guy that did my exhaust and see if he'll make any changes.

 

<div class='quotetop'>QUOTE (hamhead)</div><div class='quotemain'>If there's no CEL, then its still filtering as it should, or enough to keep the ECU's emmision standards happy, I bet its annoying though.

How long ago did you buy the cat? They go bad from running extremely rich or high exhaust gas temp in most instances. But that shouldn't be a factor if you just bought it unless it was used before or really badly designed.</div>

Not true, some cars won't throw CEL even with no cats... like mine. I still haven't gotten around to get one, and have 700mi with no cats without CEL.

 

^^ You must be burning extremely efficiently or getting good quality gas. I bet your on the threshold of pissing the O2 sensor off. tongue.gif

 

<div class='quotetop'>QUOTE (hamhead)</div><div class='quotemain'>^^ You must be burning extremely efficiently or getting good quality gas. I bet your on the threshold of pissing the O2 sensor off. tongue.gif</div>

Both most likely. I get only premium gas and probably get really good combustion smile.gif plus I use injector cleaners all the time smile.gif

So, it all depends on how good your car is running.