The catalytic converter is located in the exhaust system prior to the muffler. The catalytic converter is an emission control device added to the gasoline exhaust system to reduce hydrocarbon and carbon monoxide pollutants from the exhaust gas stream.
There are 3 types of catalytic converters: Conventional Oxidation Converters (COC), 3-Way Catalyst (TWC) and dual bed catalytic converters which are a combination of both the above mentioned. All catalytic converters are of 2 designs: a honeycomb-type block which is non-serviceable, or a small canister containing catalytic beads.
Both converters contain a base material of alumina to this also contain a material coated with platinum/rhodium. Both converters reduce hydrocarbons and carbon monoxide, while the TWC also reduces oxides of nitrogen.
Note. Use only unleaded fuel on vehicles equipped with a catalytic converter. If leaded fuel is used, coating and destruction of the catalytic surfaces will result and replacement is required.
On some models, a TWC is used in conjunction with a COC both contained in the same canister. Working in conjunction with this, there often is an air injection pipe. This pipe injects air between these 2 beds to help further oxidize the exhaust gases. This is called a dual-bed converter. (Scheme 74)
Scheme 74
On some Ford Motor Co. models, the first converter in the exhaust system is a Light Off Converter (LOC). This is a single bed type converter designed to control exhaust emissions during engine warm-up when the main converter is not at a temperature required for maximum efficiency.
On all other dual bed converter models, the first converter (3-way) in the exhaust system reduces hydrocarbons (HC) and carbon monoxide (CO), but mainly deals with oxides of nitrogen (NOx). In the second converter (oxidation type), with extra help from the air pump, reduction of hydrocarbons (HC) and carbon monoxide (CO) takes place.
HEAT SHIELDS
The combustion reaction, which is furthered by the converter, releases additional heat into the exhaust system. Temperatures in catalytic converters can reach 1600°F (870°C) under normal conditions. Special heat shields are therefore used to protect the underbody and under-vehicle components from this extreme heat.
MAINTENANCE
There is no scheduled maintenance of a catalytic converter, it is designed to last the lifetime of the vehicle. If it does not perform correctly, replace it.
RESTRICTED EXHAUST SYSTEM
A restricted or blocked exhaust system usually results in loss or lack of power or popping through carburetor. Ensure that the condition is not caused by timing or ignition problems before testing for restricted exhaust system.
- Visually inspect the complete exhaust system. If exhaust system is collapsed, replace damaged components. If exhaust system is okay, connect a vacuum gauge to intake manifold source. Connect tachometer.
- Start engine and with transmission in "Neutral" gradually increase engine speed to 2000 RPM. Check manifold vacuum reading on gauge. If manifold vacuum is greater than 16 in. Hg, exhaust system is okay.
- If manifold vacuum is less than 16 in. Hg, Turn engine off and disconnect exhaust from exhaust manifold(s). Repeat step 2). If manifold vacuum is less than 16 in. Hg, remove exhaust manifold(s).
- Check ports for casting flash by dropping a length of chain into each port. DO NOT use a wire or light to check ports, restriction may be small enough to cause excessive backpressure at high RPM.
- Check if restriction is present. If restriction is present, remove casting flash. If flash cannot be removed, replace exhaust manifold. If no restriction is present, exhaust system is okay.
- If manifold vacuum is greater than 16 in. Hg, reconnect exhaust system to manifold(s). Disconnect muffler(s). Repeat step 2).
- If manifold vacuum is less than 16 in. Hg, replace catalytic and check to ensure converter debris has not entered muffler. If manifold vacuum is greater than 16 in. Hg, replace muffler.