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.

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