bad cat?

[Bmorezcmunee]

well ive noticed my gas mileage dropping over the past few months. didnt think anything of it becuase i thought it was my air filter. change it, no difference. changed the spark plugs to iridiums and used 89 octane, no difference. then a few days ago i did a few hours of driving and there was this burning smell. then i remembered my cavalier did all these things when my catalytic converter went bad. and also the muffler started vibrating all crazy at idle on the cavalier. now the alero's muffler is doing the same thing. it also seems like the exhaust coming out is not as high pressure as it used to be. any other thoughts out there?

[CactusWill]

Yep, the rattling sound would indicate bad cat.

[[ion] C2]

sounds like it

car seem slower too?

[Beholder88]

Try running the car for a little while when it's getting dark out. Then get out and look under your car. If the cat's glowing, it's more than likely plugged, or severely restricted.

[[ion] C2]

Ah yep I monitor my catalytic converter temps in HPTuners. 1200-1400 degrees F is normal. Any hotter and likely it's restricted.

[Bmorezcmunee]

oh ok. yes it does seem slower too ion. well good thing its under warranty.