greenleg88 Posted April 13, 2009 Share Posted April 13, 2009 i posted about my 97 legacy L sedan about a week or so ago.. asking why it was so "slow".. it has a 157k miles yadi yada.. ever since i got it.. theres been a rattle at WOT... and only at WOT from about 3-4k rpm. if im driving normally in that range thers no sound... its only if i put my foot down past a certain point.. which feels like about 3/4. i forgot about it really.. and i really started to think today... and i thought perhaps its an exhaust leak.. the sound reminds me of a quieter open wastegate.... ill post a video up of the sound asap... if anyone knows what im talking id really appreciate the help. Thanks. Fred Link to comment Share on other sites More sharing options...
EVOthis Posted April 13, 2009 Share Posted April 13, 2009 your sure its not a loose heat shield? Link to comment Share on other sites More sharing options...
greenleg88 Posted April 13, 2009 Author Share Posted April 13, 2009 thats what i thought at first too.. but i feel like its not because of the way it only rattles when the pedals at the floor.. and only from 3-4k rpm..... Link to comment Share on other sites More sharing options...
greenleg88 Posted April 14, 2009 Author Share Posted April 14, 2009 http://pwnstar.rh.rit.edu/subie/2nd_gear_pull.avi http://pwnstar.rh.rit.edu/subie/1st_gear.avi here you can see that it only rattles in the certain range.. and that as long as its not at wot it doesn't rattle.. and if it is past the upper limit at WOT it still doesnt rattle. the rattle is resonating from the front passenger side.... near the floor... Link to comment Share on other sites More sharing options...
nipper Posted April 14, 2009 Share Posted April 14, 2009 When the car is cold, bang the cataytic converter with your hand. If it rattles your converter is shot. Otherwise get under the car and shake all the heat shields. I am sure you have one or more that is loose. Thats what makes a subaru a subaru nipper Link to comment Share on other sites More sharing options...
OB99W Posted April 14, 2009 Share Posted April 14, 2009 When the car is cold, bang the cataytic converter with your hand. If it rattles your converter is shot. Yes, and as CNY_Dave said in the thread concerning your car being slow, ''the catalytic converter(s) could be somewhat blocked'', so checking for that makes sense. A vacuum gauge could help determine if there's exhaust system blockage. Link to comment Share on other sites More sharing options...
greenleg88 Posted April 14, 2009 Author Share Posted April 14, 2009 hmm okay. ill try that. if my cat is shot, wouldnt i get a check engine light? assuming the o2 sensors before and after are working.... and not throwing codes. and about the cat being blocked, if this is true, would that explain why the car is "slow" because of the excess back pressure? so what if the cat was taken off, wouldnt that be not enough back pressure? i never completely understood why performance cars would take off the cats. Link to comment Share on other sites More sharing options...
OB99W Posted April 14, 2009 Share Posted April 14, 2009 if my cat is shot, wouldnt i get a check engine light? assuming the o2 sensors before and after are working.... and not throwing codes. If the catalyst isn't efficient enough, it will generate a code. However, if there's enough active surface area still available, even if loose, it won't trigger a code. and about the cat being blocked, if this is true, would that explain why the car is ''slow'' because of the excess back pressure? There's no question that excessive backpressure can reduce engine performance. A damaged cat can cause it, but so can a collapsed exhaust pipe or a muffler with a loose baffle. I once saw a car (not a Subaru) that would barely accelerate, and when the engine was revved you could actually see the muffler very slightly expand due to a blockage near its outlet. so what if the cat was taken off, wouldnt that be not enough back pressure? I don't advocate removing catalytic convertors, but the reduction in backpressure from doing so isn't a problem. For one thing, the remainder of the exhaust system (muffler, etc) provides sufficient restriction if it were needed. Furthermore, the problem with too low backpressure tended to be in the past, when modifying a car with a carbureted engine. If the backpressure was lessened enough so that the engine ran particularly lean, exhaust valves could be burned. On modern engines with engine management systems, that doesn't happen -- the ECU would just compensate. i never completely understood why performance cars would take off the cats. Doing that is probably somewhat misguided, since a cat that's not damaged is usually free-flowing enough to not greatly affect performance. Link to comment Share on other sites More sharing options...
greenleg88 Posted April 15, 2009 Author Share Posted April 15, 2009 hmm. i see. not that i plan to... but for people that do remove their cats.. how do they manage to get around emissions and the trouble codes? do they remove the first o2 sensor or put a spacer in so that it gets some cold air from outside the exhaust as well? that way there is a "temperature increase" the way there should be as if there was a cat.. or does that have an error code as well... or could a obd2 reader just clear the codes. and is that what people do right before they get their cars tested? Link to comment Share on other sites More sharing options...
nipper Posted April 15, 2009 Share Posted April 15, 2009 It depends upon the state they live in. Some states actually examin the exhaust system to make sure all the parts are there. Some people reinstall a federal exhaust system for inspection. in some states you can still use some more in$pired methods. On a modern engine its just dumb to remove the cats, as they do thier job very well, unlike the cats from the 70-80's. nipper Link to comment Share on other sites More sharing options...
greenleg88 Posted April 15, 2009 Author Share Posted April 15, 2009 When the car is cold, bang the cataytic converter with your hand. If it rattles your converter is shot. should i be expecting the first or second cat to be shot? or perhaps both? is it illegal to remove one of the two cats? just curious... ive heard of someone having the secondary one removed? would that only be half the fine since its only half the action...? hah Link to comment Share on other sites More sharing options...
nipper Posted April 15, 2009 Share Posted April 15, 2009 The 2nd cat rarely needs replacement, usually its the front one. nipper Link to comment Share on other sites More sharing options...
greenleg88 Posted April 16, 2009 Author Share Posted April 16, 2009 hmm so i banged on them both.... i guess i need to look for heat shields.... how many and about where are they? i cant put the car on a lift yet and dont really know where to start looking-i cant see any heat shield just from sitting down and looking under the car. Link to comment Share on other sites More sharing options...
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