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Old 08-14-2002, 10:38 AM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
Real Test for Catalytic Converter

my car, 89 300e failed emission test yesterday
with high amounts of HydroCarbon. my independent
mechanic insists my cat needs to be replaced.

since it is not cheap, is there a real way to test
if it is toast or not? thanks of any help.
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Old 08-14-2002, 12:08 PM
public enemy
Posts: n/a
Just to let you know, when I changed the cat in mine I went to a muffler shop and had them install a generic cat which cost me $150 including installation. It flows more than the stock cat and it costs only a fraction of the price. There is no need to buy an MB cat and spend a fortune.

Aside from that, there is no real test for cat that I am aware of.
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Old 08-14-2002, 01:31 PM
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Join Date: May 2002
Location: Mass
Posts: 1,127
The Cat should be the last resort in solving a high HC Level.
If your mechanic tested everything else, he or she is probably right.
More likely culprits are components that affect:


The Cat is only there to deal with residual gases from incomplete combustion. Reduce these residual gases, and the Cat has less 'work' to do.
Make sure your car is completely warmed up before testing to give your Cat it's best chance of keeping up.
With some work, the exhaust going into the Cat could be compared to the exhaust coming out to show whether or not it is providing an adequate reduction in HC.

This is a good link on Cats:
1986 300E 5-Speed 240k mi.
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Old 08-15-2002, 12:04 AM
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Join Date: Apr 2000
Posts: 412
a quick test can be done with a digital thermometor like those used in meat packing. In a split second it can be determined if the cat is working if the outlet side is hotter than the inlet side. I have seen it done.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T
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Old 08-15-2002, 01:15 AM
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Join Date: Jun 1999
Location: Surrey, Beautiful British Columbia, Canada
Posts: 750
thanks for all the replies and a good link.
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