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Old 07-17-2004, 04:53 PM
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Join Date: Feb 2003
Posts: 6
1976 450 SE and Catalytic Converters

My 76 450 SE just failed smog. The fellow said it was missing the cat, but my understanding was it doesn't have a catalytic converter. It passed smog in CA by the seller in LA when we bought it. A cat wouldn't have disappeared between then (last January) and now. Something is amiss. Did this model have a catalytic converter? The tag under the hood states it meets CA emission standards and says it has O/C. The last emission test in LA said it passed the visual inspection. It passes everything except the CO %. Any ideas?

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Old 07-17-2004, 05:12 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The 1976 450 was the second year to get catayltic convertors. They are not visable under the car as one would expect on all other cars including 450s from 1977 on.

They are visable under the hood as a continuation of each exhaust manifold. They are an about six inch diameter cylinder that bolts the the flat front of the manifold and extend to the back of the engine and decend like a normal down seciton of the manifold. They are built in such a way that one could take the manifold and converter off and replace it with a 1974 manifold and no one would be the wiser. From the exhaust port to the exhaust pipe the 74 manifold completely replaces the rig that is manifold and cat on a 75-76 model.

If you are failing the test (and do have cats) you might not have sufficient air pump function as those cats were just oxidation cats and they needed induced oxygen to function.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 07-17-2004, 05:43 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,538
1975 and 1976 were the only two years that 450 SL's and 450 SEL's had the catalytic converters in the engine bay.

It was a total disaster. Having the cats in the engine compartment caused vapor lock problems because air flow was restricted by the tight fitting engine underhood. Excess heat also baked wires and hoses.

I wonder if you could move the cats to the typical place underneath the car....

Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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