I bought a catalytic converter less than 2 years ago and already its rattling. I have recently replaced the valve seals and the valve cover gasket, and I am going to have the fuel mixture checked when I replace the cat. Is there anything else I should check that might have caused it to fail so quickly? Car is a '90 560SEL. Thanks for any input.

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90 560SEL
H&R springs
17" Alba Frontiers
Cross drilled rotors
Magnaflow Cat
European Headlights
WALD front bumper
Keyless Entry
Burlwood shiftknob
Clear corners, taillights
Limo tint
2 JL 12W6's, JBL BP1200.1, Pioneer P8200R

Short trips where it does not get up to temp before the car is shut down again and improper fuel mixture.

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Jim

Are you sure it's not just the shield that rattles?

Freestyler

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Never criticize someone until you've walked a mile in his shoes. That way, when you do, you're a mile away -and you have his shoes!


'86 300E optically converted to '95 E300 (Sold)
-Blauschwarz on silver
-Black leather
-17" AMG & 15" AMG for winter

Converter failure can be caused by:
1. Constant misfiring ( overloads & overheats ) the converter.
2. Excessive oil consumption.

I have seen total converter meltdown in 50 miles, due to a faulty coilwire ( GM ).

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2007 C 230 Sport.

Among other reasons, there is great likelyhood that the replacement cat wasn't a genuine MB part. The MB catalyst is about 10 times better made than any aftermarket version. Based on that alone two years isn't bad.

But as others have said a cat can be damaged in 50 miles of meltdown conditions. Those are such when closed loop fuel control is not strictly maintained.

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

some of these aftermarket cats are just plain junk. catco is one i can think of in so. cal. there is nothing like a factory cat for most cars. a lot of cats are replaced because fuel mixture was wrong,too rich, which shut down the cat. fix the mixture problem ,take tailpipe readings and the cat is not working.drive the car 20-100 miles and the cat will come back to life. readings are like a new car. this does not happen much because customer wants instant results, not maybe it will come back.
also they wait till the last minute. smog due yesterday. as soon as an aftermarket cat goes on a car ,there is a good chance it will need a new one next smog check. the nox part of these cats are weak.at least half the time the cat was put on with out fixing the fuel mix problem,so again new cat next time.
sorry bout this long reply. the other responses where also right on. try to save the factory cat.
while dealing with cats, a lot of techs are not aware that obd2 fuel mix MUST go rich to lean at a fast pace, if biased rich or lean the nox part of the cat does not work very well. the mix has to cross over the stoich point for the cat to save then use oxygen for nox reduction. biased o2 sensors make the cat look bad. got carried away here thanks rich

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88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car

All of you are correct, it is an aftermarket "high flow" cat made by Magnaflow. I am pretty sure my fuel mixture is rich so I will have that checked. Olpos, is it really true that if I fix everything that the cat can come back to life? Thanks for the quick responses.

__________________
90 560SEL
H&R springs
17" Alba Frontiers
Cross drilled rotors
Magnaflow Cat
European Headlights
WALD front bumper
Keyless Entry
Burlwood shiftknob
Clear corners, taillights
Limo tint
2 JL 12W6's, JBL BP1200.1, Pioneer P8200R

If it's rattling it isn't likely to resecure itself.

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

also a bad O2 Sensor will harm the cat convertor

Both cats went on the Range Rover due to the use of regular (87 octane) gas when it requires premium (93). [Before i purchased] I believe it is the same in the MB. When they went on the Rover, it sounded like the engine was rapping real bad.

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro

Why? Did the 87 have lead in it?

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2012 E350
2006 Callaway SC560

if your cat is broken you will have to replace it cause the noise will make you crazy.some cats that are broken will still work enough to pass another smog check. the piece inside may be in two large chunks or may be small enough to get inside the resanator or muffler. this leaves you with more rattles.
when the mixture is correct what is inside your cat will clean up and you will get your best numbers possible.
i have seen a lot of broken cats pass the test. but what about the chunks inside. do you really want them in your muffler?
fix the mixture problem,drive a hundred miles and retest. this will tell you what to do next. good luck
food for thought and maybe a different tread. this timing resistor that is removed for power, what if a resistor that retarded your timing more, instead of less was made and put in before a smog check. that should improve all the tailpipe numbers.
this would be for cars that almost pass smog.
nox,co and hc would go down. will experament with this soon. tail pipe numbers with and without the resistor.
got carried away again rich

__________________
88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car

o2 sensors can be working when you check them or be out of range. if its old and can be found at a good price, then change it. some times all the checks you do just don't catch it acting up.
plus a new sensor works a lot faster. don't forget to verify that the new sensor works. even new parts can be dead.
buy the bosch brand . less problems
rich

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88 300E White, sold 9-04
88 190E Black 2.3 sold
90 300CE White, Grey sold 12-24-04
92 400E White,Grey Sold 5-06
90 300CE 91K Signal Red,Black Sold 2007
1989 300CE Smoke silver,Tan Sold 1-08
1993 300E 3.2 M104 motor
1991 300CE White,Grey
1994 E420 beautiful car,gone to new home
1994 E320 Smoke an Parchment.Beautiful car

I had a mechanic raise the car up, he thought it failed because my car is lowered and I scraped on it too much. There was quite a few scartch marks on it, but but I have never hit it hard. I always go over bumps real slow and rarely does it ever bottom out. If this is the case though I will just remove the cat and put it back on when smog time comes around. $350 for installed cat vs 50-100 for installation and removal every 2 years... Depends on how the O2 sensor is. olpus let us know how your experiment goes, sound interesting.

__________________
90 560SEL
H&R springs
17" Alba Frontiers
Cross drilled rotors
Magnaflow Cat
European Headlights
WALD front bumper
Keyless Entry
Burlwood shiftknob
Clear corners, taillights
Limo tint
2 JL 12W6's, JBL BP1200.1, Pioneer P8200R

i recently failed my emissions test in texas...my check engine light is not on, i can't afford to take it to the dealer to diagnos the problem, here is what i failed:

Low Speed Emissions Result:
HC 825 (standard 220)
CO 8.3 (standard 1.20)

I was told it was either my cat or my o2 sensors...any help please!!!!