A catalytic converter is a device located in the exhaust system of all cars and most light trucks after 1990. It chemically changes pollutants like carbon monoxide hydrocarbons and nitrous oxides into harmless substances like carbon dioxide, nitrogen and water vapour. A converter uses an inside structure called a substrate that is plated with precious metals such as platinum, palladium and rhodium. These elements cause the chemical change.

TESTING CONVERTERS

THE THUMP TEST:
Thump the converter with your fist. If it is a monolith type and you hear pieces moving around inside the converter chances are the substrate has come apart.

THE TEMPERATURE TEST:
For this test you will need a digital pyrometer. To commence testing, run the vehicle at a high rpm for two minutes (about 2,000 rpm). This needs to be done to ensure that the converter has had time to activate. Touch the probe of the pyrometer to the front of the converter and note temperature. Touch the probe to the rear of the converter and note temperature. There should be a noticeable difference between the two temperatures, with the rear temperature being hotter. If the rear is not hotter than the front, the converter is not working properly.

THE BACK PRESSURE TEST:
This test will require a back-pressure gauge. An inexpensive back-pressure gauge can be made from a small pressure gauge that reads from 0 to 30 psi, a piece of vacuum tubing and a small 3 mm 0.D. piece of copper tubing with a 3 mm l.D. viton 0-ring. This 0-ring will help to seal the hole that the copper tube is inserted into, or a back-pressure gauge may be purchased from numerous sources pre-made. The exhaust pipe at the front of each converter. With the engine running, check the back pressure. The back pressure should be no more than 4 to 5 psi. This reading is with the throttle partly open at 2500 rpm. When checking exhaust back pressure, be sure to check at the inlet and outlet of each converter or exhaust component tested. A reading of 1/2 to 2 psi is normal.

EXHAUST GAS ANALYSER TEST:
A gas analyser will tell you if the converter is functioning properly. By checking your CO (carbon monoxide) reading, you will also be able to tell if the system is operating rich. Hooking up the machine differs according to the model and brand of analyser being used. Consult the analyser manual for instructions. Once you have determined that the converter has failed, the next step should be to find out why it failed.