Figure 24. 1 Typical catalytic converter Figure 24.1 Typical catalytic converter. The small tube into the side of the converter comes from the air pump. The additional air from the air pump helps oxidize the exhaust into harmless H2O and CO2.

Figure 24.2 A typical catalytic converter with a monolithic substrate.

Figure 24.3 The three-way catalytic converter first separates the NOx into nitrogen and oxygen and then converts the HC and CO into harmless water (H2O) and carbon dioxide (CO2).

Figure 24.4 A cutaway of three-way catalytic converter showing the air tube in the center of the reducing and oxidizing section of the converter. Note the small holes in the tube to distribute air from the AIR pump to the oxidizing rear section of the converter.

Figure 24.5 The OBD-II catalytic converter monitor compares the signals of the upstream and downstream O2Ss to determine converter efficiency.

Figure 24.6 The waveform of an O2S downstream from a properly functioning converter shows little, if any, activity.

Figure 24.7 The highest catalytic converter efficiency occurs when the air-fuel mixture is about 14.7:1.

Figure 24.8 A catalytic converter that rattles when tapped was removed and the substrate, or what was left of it, fell out. This converter has to be replaced and the root cause of why it failed found and corrected.

Figure 24.9 A back pressure tool can be easily made by attaching a short section of brake line to the shell of an old oxygen sensor. Braze or epoxy the tube to the shell.

Figure 24.10 A photo of a partially melted catalytic converter that tested okay at idle but had excessive back pressure at idle speeds.

Figure 24.11 The temperature of the outlet should be at least 10% hotter than the temperature of the inlet. This converter is very efficient. The inlet temperature is 450°F.Ten percent of 450° is 45° (45° + 450° = 495°). In other words, the outlet temperature should be at least 495°F for the converter to be considered okay. In this case, the outlet temperature of 525°F is more than the minimum 10% increase in temperature. If the converter is not working at all, the inlet temperature will be hotter than the outlet temperature.

Figure 24.12 Whenever replacing a catalytic converter with a universal unit, first measure the distance between the rear brick and the center of the rear oxygen sensor. Be sure that the replacement unit is installed to the same dimension.