Mercury 9L8Z-5G232-A Exhaust Manifold And Catalyst Assembly

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A catalytic converter (or catalyst) is an emission control device in the exhaust system that reduces certain pollutants in the exhaust gas stream. There are two types of converters: an oxidation catalyst, which reduces hydrocarbons (HC) and carbon monoxide (CO), and a reduction catalyst, which reduces oxides of nitrogen (NOx). Catalysts that can reduce all three pollutants are known as "three-way catalysts." The models covered by this manual are equipped with three-way catalysts.

Check the manifold for warpage and have it resurfaced if necessary.

Remove the exhaust manifold and its gasket, discarding the gasket, and also remove and discard the exhaust manifold mounting studs.

Use a straightedge and feeler gauge to inspect the exhaust manifold mating surface for warpage. If warpage exceeds limits, replace or resurface the manifold or cylinder head.

Although catalytic converters don't break too often, they can become clogged or even plugged up. The easiest way to check for a restricted converter is to use a vacuum gauge to diagnose the effect of a blocked exhaust on intake vacuum.

Use a scraper to remove all gasket material and carbon deposits, being careful not to gouge the aluminum engine parts.