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Guest Message by DevFuse

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Bat Catalytic converter?

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5 replies to this topic

#1 crazyman03


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Posted 14 August 2013 - 08:47 PM

So I've been hearing a fluttering type sound going on that I origionally thought was just a leak. I plugged what leaks I did find, I even got some muffler mud and flat-out sealed the flange from the Cat back. (there are no other flanges beyond that). 


I still hear the fluttering and Its coming from the catalytic area. the only thing i havent done is pull the shroud around  the cat off and visually *look* but was curious if this may sound like a bad cat or not... It kinda seems like there is a lack of power at times. My average mpg is 23 city and about 26-27ish highway.



the fluttering kinda gets softer/quieter the hotter of a day it is and when i've been driving a bit. 






#2 Rooster2


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Posted 15 August 2013 - 06:35 PM

What year and model car do you have? Knowing that, I have some thoughts.......

#3 crazyman03


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Posted 15 August 2013 - 08:16 PM

95 impreza.. ej22 auto

#4 Rooster2


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Posted 15 August 2013 - 10:36 PM

Sounds like a typical exhaust leak to me. Doubt that it comes from the cat as they are really made of tough material, and don't split open to leak. Both of my Leggie Outbacks (98 & 99) developed leaks at the end of the resonator. All Subie exhaust systems are pretty much the same design. The resonator is located just after the cat. I had a muffler shop cut off the resonator, and weld in a piece of straight pipe. The result is great. Just as quiet as can be. Don't know why Subaru has a resonator in the exhaust system.


I look for exhaust leaks by crawling underneath the car the best I can. I have even driven two side wheels up over a curb, with the other two wheels still on the street. This can make it easier to crawl underneath, as the car gets raised a bit doing this. Just be sure to put on the parking brake before crawling underneath with the engine running at idle. The exhaust leak noise will pretty quickly lead you to where the leak is. Yes, the shrouds can sometimes be in the way, and sometimes the leak can be at the top of the pipe, so it is out of sight. Feel around the pipes, wear mechanics gloves to keep from getting burned from the hot pipes.


Let us know what you find out.

#5 MilesFox


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Posted 15 August 2013 - 10:50 PM

I would suspect either the flange gaskets between the cats are rusting through, or where may be a crack developing just aft of the rear cat where the pipe comes out.

#6 steveb3


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Posted 04 September 2013 - 11:06 PM

Ive followed this thread because I've had a similar experience. I just  had short block,tensioner and cat replaced on my 06 Leg 2.5i.It just turned 150k Short block from loss of power and slivers in oil, cat for exhaust leak(not heard but detecteded by tech) and tensioner because of oil leakf rom around it. The head gaskets were replaced too. After it was done,the pick up was back and mpg back to normal, but there was some tap that wasn't there before. It was determined by my tech, who is Subie certified and works at a local dealership, that the injectors sounded clogged. He then did a injector cleaning and the tap was gone. But now after all that, there seems to be a rattle when accelerating at about 20-40 mph coming from the drivers side. We checked and tightened all heat shields so that is ruled out. It sems to be more noticeable after warm up and the noise seems to be in sync with the RPMs, sounding like a quicker rattle at higher RPM.But it doesn't throw a code or affect performance. It's more annoying than anything else,just loud enough to be heard.I've read it could be exhaust leak, maybe a bad new cat? Any ideas? Thanks Steve

Edited by steveb3, 04 September 2013 - 11:08 PM.

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