Lexus 25052-20020 Exhaust Manifold Converter Sub-Assembly, No.2

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The catalytic converter is an emission control device in the exhaust system that reduces pollutants. There are two types: oxidation catalyst, which reduces HC and CO levels, and three-way catalyst, which also decreases NOx. Checking the converter requires expensive equipment. During underbody servicing, inspect for leaks, corrosion, and damage. If any damage is found, replace the converter. To diagnose a restricted converter, use a vacuum gauge to assess the impact of a blocked exhaust on the intake vacuum. Connect the gauge to a vacuum source, warm the engine, and note the vacuum reading at idle and after opening the throttle. If the reading is more than one in-Hg lower after the fourth test, there may be a restriction. When replacing the converter, spray the nuts on the exhaust flange studs before removing them, and then proceed to remove the nuts and separate the converter from the exhaust system. The installation process is the reverse of the removal procedure.

Disconnect the negative cable from the battery. Spray penetrating oil on the exhaust manifold fasteners and allow it to soak in. Remove the heated oxygen sensors from the front and rear manifolds. Remove the EGR pipe from the rear exhaust manifold and cylinder head. Remove the nuts retaining the exhaust pipes to the front and rear exhaust manifolds. Disconnect the electrical connector from the oxygen sensor at each manifold. Unbolt the exhaust manifolds from the cylinder heads and slip them off the mounting studs. Carefully inspect the manifolds and fasteners for cracks and damage. Use a scraper to remove all traces of old gasket material and carbon deposits from the manifolds and cylinder head mating surfaces. If the gasket was leaking, check the manifolds for warpage on the cylinder head mounting surface by placing a straightedge over the surface and trying to insert a feeler gauge. If the clearance exceeds the limit, have the manifold resurfaced at an automotive machine shop. Position new gaskets over the cylinder head studs. Install the manifolds and thread the mounting nuts into place. Working from the center out, tighten the nuts. Reinstall the remaining parts in the reverse order of removal. Use new gaskets when connecting the exhaust pipes. Run the engine and check for exhaust leaks.

The marks on the gasket should face out (away from the head) and the arrow should point toward the rear (transaxle end) of the engine.