Your Subaru catalytic converter is responsible for transforming toxic byproducts of combustion in the exhaust into less-toxic substances by way of catalyzed chemical reactions. Because of its importance, driving a car without this component has been made illegal in the United States. In order for you to stay out of trouble, be on constant alert for signs of a failing catalytic converter. Here are some problems that you may encounter:
The most common cause of catalytic converter failure is congestion, as this usually happens in older cars. Over time, this component can become so clogged that the exhaust gases can't get through it. If air can't get out of the rear of your car, new air can't flow into the front end either. Because no air is coming in to form the fuel/air mixture in the exhaust, the engine then dies.
A clogged catalytic converter is not the only cause for the component's failure; a contamination in the catalyst can cause it to go bad as well. If this happens, high carbon monoxide (CO) and hydrocarbon (HC) gases will be present in the exhaust system.
To confirm this diagnosis, use a high-temperature digital pyrometer-or an oven thermometer if you don't have access to the first tool. With this, check the catalytic converter's temperature before and after you start the engine. If the component runs 100 degrees Fahrenheit hotter at its outlet than at its inlet, then it is still good. However, if there is little- to no-temperature change, either your car has a problem with low efficiency or it has a problem with the catalytic converter's air supply.
Inspect the air injection pump, belt, and check valve as well. If you think that the check valve is allowing the exhaust to flow backwards, then remove it and blow through both ends. It should let air pass only in one direction but not in the other.
Examine the air injection manifold, too, because it tends to rust and leak air. Lastly, check the diverter valve to make sure it is working correctly. It should be routing air to the converter when the engine is at normal temperature.