If I put some rocks and fender washers in the dryer....

[unobtainium]

that would be the sound my 1993 Legacy wagon (AWD, 5MT) makes -sometimes- on deceleration. It is an amazing noise. It seems to have something to do with the catalyst or something in the front exhaust pretty near there - if I push down on the front cat while the noise is happening (off-idle but stationary) the noise can be made to come and go.

 

I checked underneath the car to see if I could find a problem - and I can't see anything wrong.

 

Is it possible that when the catalyst is shot, bits get loose in there that can make this noise?

 

Thanks -

 

Greg

[frag]

What about the heat shields and specialy those covering the pipes connecting to the cat and the cat itself? Hope it's that cause a new cat costs.

[meep]

sounds like you're back firing during deceleration, and you're hearing it muffled inside the exh system. When's the last time you had a tune up, plugs, top end cleaned, etc. Could also try higher octane fuel.

 

Mike

[alias20035]

Likely to be:

 

1. loose heat shields, create some wedges of aluminum foil and jam between exhaust pipe and all loose heat shields. This trick is cheaper, easier and more effective than new shields and brackets.

 

2. bad donut exhaust gasket. With the engine running have a friend plug the tailpipe with a rag and hand. Any exhaust leak should show up. But the donut gasket is the most common problem. During deceleration the exhaust system tilts in relation the engine and Y pipe causing a "backfire" like sound. I had this problem three times on my 85 Subaru, I don't even recall if my 93 even had a donut gasket. If it does it is a potential source of the problem.

 

3. bad exhaust gaskets or loose studs on the heads of the engine, quite common and cheap to repair, just be sure to use new exhaust studs and bolts, properly torque them and ALWAYS do this work with the engine cold to avoid stripping the threads in the head.

 

4. cracked Y pipe. I had a cracked Y pipe on my 1993 Legacy, just below the passenger's side of the engine where the 2 pipes from each cylinder joined into 1. Dealer quoted $700 for new Y pipe/cat assembly, I took the car to Midas and had it welded for $40, no more problem for 5 more years. Water and slush spray from the tire caused this problem, which initially only occured in wet weather and then it completely failed. You should be able to find this with the rag in the tailpipe method. Cracked Y pipes on earlier Legacys are common, in 95 or 96 Subaru changed the assembly so that a cracked Y pipe did not require the replacement of the cat as well.

 

5. engine out of tune, possible but other than spark plug changes, Legacy's tune themselves. Given the age of the exhaust system, it is likely to be cause 1 thru 4 so look there first.

 

Cats either fail to purify the exhaust (Service Engine light or failed emmisions test) or they plug up (engine wont start or runs badly). Since you are complaining about "backfiring" like noises and not lost power, your cat is not the source of the problem unless it has a hole in it.

[unobtainium]

Went underneath the car and banged on things. The cat goes bzz, bzz when I hit that. Nothing else makes any noise at all.

 

Took heatshields off the cat, removed two small rocks and re-tried. Things are the same.

 

I haven't tried the rag + hand test alias mentioned, when I have those results I'll be back.

 

Thanks, all.

 

-Greg

[theotherskip]

i tried fixing it by banging around with the car off, and got no results. i finally jacked the car, had a friend rev the engine while i pressed on the different heat shields while wearing thick gloves. i found the one that was rattling (the one before the cat), then let it all cool. i removed the heat shield, bent the clamps so that they would grab the pipe tighter (they were loose when i started), and the noise is now gone...