Catalytic converter diagnosis

Catalytic Converters have been in use in Australia since the introduction of un-leaded petrol in 1986.
Three way catalytic converters are designed to convert 3 toxic substances (Oxides of Nitrogen, Carbon Monoxide and Hydrocarbons) out of vehicle exhaust emissions into non-toxic substances.

Oxides of Nitrogen are a major contributor to photochemical smog.
The Catalytic Converter converts these to Nitrogen and Oxygen.
Carbon Monoxide can be fatal if inhaled.
The Catalytic Converter converts this to Carbon Dioxide.
Hydrocarbons are unburned fuel.
The Catalytic Converter converts these to water vapour. Should the Catalytic Converter become damaged or worn out, these 3 toxic substances pass through the exhaust into the atmosphere.
Catalytic Converters are not mufflers.
They incorporate ceramic bricks into which has been embedded precious metals.
As these metals are not distributed uniformly, the direction of gas flow is critical to correct operation.
Where the Catalytic Converter can be accidentally reversed, the direction of flow is indicated by an arrow on the body or heat shield.
Accident damage or excessively rich air/fuel mixtures (can be caused by a fouled spark plug or faulty ignition lead) can cause the Catalytic Converter to melt down (the catalyst melts and breaks up).
This can block the exhaust system causing power loss, stalling and backfiring.
Most Catalytic Converter failure can be attributed to improper engine tuning, incorrect ignition timing or fouled spark plugs.

Testing Catalytic Converters

To test for blockage, Access a pressure point before the catalytic converter, install a back pressure gauge and measure the back pressure. Normal reading should be less than 9 kPa @ idle and less than 20 kPa @ 2500 RPM. A high reading indicates the catalytic converter may be damaged or blocked.
To test efficiency, Hold the engine speed at 2500 RPM for several minutes to heat up the catalytic converter and allow engine to idle. Using a pyrometer (high temperature thermometer), measure the temperature of the exhaust pipe around 50 mm before and after the catalytic converter. The outlet temperature should be at least 40°C hotter than the inlet temperature. If not, the catalytic converter may be faulty.

After Market Catalytic Converters

The most common aftermarket catalytic converter in Australia is the three way. They can be used in place of both two way and three way original catalytic converters. After market catalytic converters are accepted by the EPA in Victoria and New South Wales as long as they are marked confirming their conforming to the California State approval code.
The code on the first line should begin with CA (Californian Approval).
The numbers on the third line indicate whether it is a two way, three way or three way with air type (check with the manufacturers catalogue).