I've got a 97 SL500 with 60k. It makes a knocking sound during deceleration. The car runs fine. Is this a cat problem?

Thanks,
Lyndon Tilson

Haven't seen many late model MB cats fail in that way. The BMW V8 has that happen all the time.

My main reason for answering is that you might not know that your catalysts are probably still in emissions warrantee. (8year? 80,000 miles) (not sure about the time but just had one of my 540i cats done a few months ago under warrantee (97 540i 51k miles).

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Just a cheap suggestion before the big expense!

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J.H.
'86 300E

Thanks for the hanger suggestion, but unfortunately its definately an internal knock.

lyndongt

I had a bad CAT on a 1998 E320 that was fixed about 6 months ago under the 8/80000 federal emissions warranty after some discussion with the service supervisor who initially said it was not covered; but, we got it all sorted out.

It took me a few service visits to get it identified because it NEVER happened when I left the car. I made arrangements to drive with the service manager. This way I could ensure the problem was occuring.

Mine only did it when the car was VERY warm from driving on the expressway. Even idleing for a mere five minutes gave the CAT enough time to cool down and eliminate the problem. When it was WARM I could just lightly rev the motor and it would rattle every time the motor was idleing down.

Just find a protocal where you can consistently reproduce the problem and meet with service manager. I went as far as to video tape (with sound) how I reproduced the problem so at least the mechanic knew I wasn't imagining this it case it decided not to act up.

Good luck,

Intruder