Ford AL8Z-5G232-A Exhaust Manifold And Catalyst Assembly

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.

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".

Connect a vacuum gauge to an intake manifold vacuum source. Warm the engine to operating temperature, place the transaxle in Park (automatic models) or Neutral (manual models), and apply the parking brake. Note the vacuum reading at idle and jot it down. Quickly open the throttle to near its wide-open position and then quickly get off the throttle and allow it to close. Note the vacuum reading and jot it down. Repeat this test three more times, recording your measurement after each test. If your fourth reading is more than one in-Hg lower than the reading noted at idle, the exhaust system might be restricted, indicating that the catalytic converter could be plugged, or an exhaust pipe or muffler could be restricted.

Raise the vehicle and place it securely on jackstands.