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Catalytic converters replaced and now things are loud

780 views 3 replies 4 participants last post by  Mustang5L5 
#1 ·
Generally you wouldn’t think that being loud would be an issue for a mustang - but it sounds bad. Last month Sun Auto replaced the catalytic converters in my stock 2008 Bullitt. Now the engine sounds really loud when I start it up. Louder than ever before. At first it was just loud at under 20 mph or so. Now it’s loud all the way through 85+. Acceleration seems down too. Do I take it back to them for the 3rd time, or is there a wearing in period for the converters? Thanks.
 
#2 ·
Loud at the end of the tailpipe? Loud under the car? Could it be an exhaust leak? Have you tried to diagnose where the "loudness" is coming from?

Joined 2011 and 1st post? Wow. Welcome?!
 
#3 ·
Not sure what brand of cats they used, but there is no break in period that I've ever heard of.

If you like the sound of the stock cats, I'd assume you could locate a stock "take-off" h-pipe with low miles in the classifieds, craigslist or eBay and get them to install that.
 
#4 ·
Cats don't really "break in". Sounds like this is just an issue of aftermarket high flow cats vs stock cats? That is assuming, of course, the exhaust shop did a good job fully welding things up and there are no leaks and such.

Acceleration being down might be sign of a big leak as well. Can you have them check to see if there is a leak upstream of the cat?
 
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