objectives

Advanced Engine Performance Diagnosis, 4/eBy James D. Halderman

OBJECTIVES

After studying Chapter 24, the reader will be able to:

1. Prepare for ASE Engine Performance (A8) certification test content area “D” (Emission Control Systems).

2. Describe the purpose and function of the catalytic converter.

3. Discuss how the catalytic converter is tested under OBD-II regulations.

4. Explain the method for diagnosing and testing the catalytic converter.

CATALYTIC CONVERTERS

• A catalytic converter is an after-treatment device used to reduce exhaust emissions outside of the engine.

• This device is installed in the exhaust system between the exhaust manifold and the muffler, and usually is positioned beneath the passenger compartment.

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.

CERAMIC MONOLITH CATALYTIC CONVERTER

FIGURE 24-2 A typical catalytic converter with a monolithic substrate.

CERAMIC MONOLITH CATALYTIC CONVERTERCatalytic Converter Operation

• The converter contains small amounts of rhodium, palladium, and platinum.

• These elements act as catalysts. – A catalyst is an element that starts a chemical reaction

without becoming a part of, or being consumed in, the process.

– In a three-way catalytic converter (TWC), three exhaust emissions (NOX, HC, and CO) are converted to carbon dioxide (CO2) and water (H2O).

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.

CERAMIC MONOLITH CATALYTIC CONVERTERConverter Light-Off

• The catalytic converter does not work when cold and it must be heated to its light-off temperature of close to 500°F (260°C) before it starts working at 50% effectiveness.

CERAMIC MONOLITH CATALYTIC CONVERTERConverter Usage

• A catalytic converter must be located as close as possible to the exhaust manifold to work effectively.

• The farther back the converter is positioned in the exhaust system, the more gases cool before they reach the converter.

CATALYTIC CONVERTER WARM-UP TEST

• The PCM determines if the catalytic converter is ready for testing based on the following conditions, which may vary by vehicle make, model, and year.– Closed-loop status achieved– IAT sensor temperature higher than 32°F (0°C)– ECT sensor temperature higher than 165°F (18°C)– MAF sensor input from 15 to 32 g/sec– Engine load less than 65% and steady– Engine speed less than 4000 RPM– All of the above conditions met for at least four minutes

OBD-II CATALYTIC CONVERTER PERFORMANCE

• With OBD-II equipped vehicles, catalytic converter performance is monitored by a heated oxygen (HO2S) sensor both before and after the converter.

FIGURE 24-5 The OBD-II catalytic converter monitor compares the signals of the upstream and downstream O2Ss to determine converter efficiency.

OBD-II CATALYTIC CONVERTER PERFORMANCE

FIGURE 24-6 The waveform of an O2S downstream from a properly functioning converter shows little, if any, activity.

CONVERTER DAMAGING CONDITIONS

• The three main causes of premature converter failure are as follows:– Contamination. – Excessive temperatures. – Improper air-fuel mixtures.

FIGURE 24-7 The highest catalytic converter efficiency occurs when the air-fuel mixture is about 14.7:1.

DIAGNOSING CATALYTIC CONVERTERSThe Tap Test

• The simple tap test involves tapping (not pounding) on the catalytic converter using a rubber mallet.

• If the substrate inside the converter is broken, the converter will rattle when hit.

• If the converter rattles, a replacement converter is required.

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.

DIAGNOSING CATALYTIC CONVERTERSTesting Back Pressure with a Vacuum Gauge

• A vacuum gauge can be used to measure manifold vacuum at a high idle (2000 to 2500 RPM).

• If the exhaust system is restricted, pressure increases in the exhaust system.

• This pressure is called back pressure. • Manifold vacuum will drop gradually if the engine is

kept at a constant speed if the exhaust is restricted.

DIAGNOSING CATALYTIC CONVERTERSTesting Back Pressure with a Pressure Gauge

• Exhaust system back pressure can be measured directly by installing a pressure gauge in an exhaust opening.

• This can be accomplished in one of the following ways.– To test an oxygen sensor, remove the inside of an old, discarded

oxygen sensor and thread in an adapter to convert it to a vacuum or pressure gauge.

– To test an exhaust gas recirculation (EGR) valve, remove the EGR valve and fabricate a plate.

– To test an air injection reaction (AIR) check valve, remove the check valve from the exhaust tubes leading to the exhaust manifold.

• Use a rubber cone with a tube inside to seal against the exhaust tube. • Connect the tube to a pressure gauge.

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.

DIAGNOSING CATALYTIC CONVERTERSTesting a Catalytic Converter for Temperature Rise

• A properly working catalytic converter should be able to reduce NOX exhaust emissions into nitrogen (N) and oxygen (O2) and oxidize unburned hydrocarbon (HC) and carbon monoxide (CO) into harmless carbon dioxide (CO2) and water vapor (H2O).

DIAGNOSING CATALYTIC CONVERTERSTesting a Catalytic Converter for Temperature Rise

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.

DIAGNOSING CATALYTIC CONVERTERSCatalytic Converter Efficiency Tests

• The efficiency of a catalytic converter can be determined using an exhaust gas analyzer.– Oxygen level test.

• If O2 is zero, go to the snap throttle test.

• If O2 is greater than zero, check the CO level.

• If CO is greater than zero, the converter is not functioning correctly.

– Snap-throttle test.• The O2 reading should not exceed 1.2%; if it does, the converter is not

working.

• If the O2 rises to 1.2%, the converter may have low efficiency.

• If the O2% remains below 1.2%, then the converter is okay.

AFTERMARKET CATALYTIC CONVERTERS

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.

OBD-II CATALYTIC CONVERTER MONITOR

• The catalytic converter monitor of OBD-II uses an upstream and downstream HO2S to test catalytic efficiency. – When the engine combusts a lean air-fuel mixture, higher

amounts of oxygen flow through the exhaust into the converter.

– The catalyst materials absorb this oxygen for the oxidation process, thereby removing it from the exhaust stream.

CATALYTIC CONVERTER REPLACEMENT GUIDELINES• Because a catalytic converter is a major exhaust gas

emission control device, the Environmental Protection Agency (EPA) has the following strict guidelines for its replacement.– If a converter is replaced on a vehicle with less than 80,000 mi/eight

years, depending on the year of the vehicle, an original-equipment catalytic converter must be used as a replacement.

– The replacement converter must be of the same design as the original. If the original had an air pump fitting, so must the replacement.

– The old converter must be kept for possible inspection by the authorities for 60 days.

– A form must be completed and signed by both the vehicle owner and a representative from the service facility.

CATALYTIC CONVERTERRELATED DIAGNOSTIC TROUBLE CODE

CATALYTIC CONVERTER OPERATION

SUMMARY

1. A catalytic converter is an aftertreatment device that reduces exhaust emissions outside of the engine.

2. The honeycomb shape of the catalytic converter is constructed of a ceramic material about 0.006 in. thick with small square openings.

3. A catalyst is an element that starts a chemical reaction but is not consumed in the process.

4. The catalyst materials used in a catalytic converter include rhodium, palladium, and platinum.

SUMMARY

5. A catalytic converter has to be over 500°F (260°C) before it starts to become effective, and is therefore mounted as close as possible to the exhaust parts of the engine.

6. The OBD-II system monitor compares the relative activity of a rear oxygen sensor to the precatalytic oxygen sensor to determine catalytic converter efficiency.

7. Catalytic converters can be tested for restriction and for efficiency.

REVIEW QUESTIONS

1. What are the three most commonly used catalysts used in a catalytic converter?

2. How does a catalytic converter reduce NOX to nitrogen and oxygen?

3. Why must a catalytic converter be mounted close to the exhaust ports of the engine?

4. How does the computer monitor catalytic converter performance?

5. What tests can be performed by a service technician to test the catalytic converter?

6. What precautions should be adhered to when installing a universal fit catalytic converter?

CHAPTER QUIZ

1. What is applied to the ceramic substrate to make the surface porous?a) Honeycomb filler

b) Washcoat

c) Aluminum

d) Cerium

CHAPTER QUIZ

1. What is applied to the ceramic substrate to make the surface porous?a) Honeycomb filler

b) Washcoat

c) Aluminum

d) Cerium

CHAPTER QUIZ

2. Two technicians are discussing catalytic converters. Technician A says that the exhaust mixture must be at stoictiometric for the best efficiency. Technician B says that the air-fuel mixture must be leaner than 14.7:1 for best performance from a three-way catalytic converter. Which technician is correct?a) Technician A only

b) Technician B only

c) Both Technicians A and B

d) Neither Technician A nor B

CHAPTER QUIZ

2. Two technicians are discussing catalytic converters. Technician A says that the exhaust mixture must be at stoictiometric for the best efficiency. Technician B says that the air-fuel mixture must be leaner than 14.7:1 for best performance from a three-way catalytic converter. Which technician is correct?a) Technician A only

CHAPTER QUIZ

3. A catalytic converter has to be at least how hot before it starts to work?a) 500°F (260°C)

b) 1,000°F (540°C)

c) 1,500°F (815°C)

d) 2,000°F (1,100°C)

CHAPTER QUIZ

3. A catalytic converter has to be at least how hot before it starts to work?a) 500°F (260°C)

b) 1,000°F (540°C)

c) 1,500°F (815°C)

d) 2,000°F (1,100°C)

CHAPTER QUIZ

4. What two primary sensors does the PCM use to check the catalytic converter?a) Catalytic converter temperature sensor and rear oxygen

sensor

b) Precat and postcat oxygen sensor

c) Precat oxygen sensor and MAF

d) MAP and TP

CHAPTER QUIZ

4. What two primary sensors does the PCM use to check the catalytic converter?a) Catalytic converter temperature sensor and rear oxygen

sensor

b) Precat and postcat oxygen sensor

c) Precat oxygen sensor and MAF

d) MAP and TP

CHAPTER QUIZ

5. A catalytic converter can be harmed by _____.a) Excessive engine oil

b) Antifreeze

c) Sulfur from poor-quality fuel

d) Any of the above

CHAPTER QUIZ

5. A catalytic converter can be harmed by _____.a) Excessive engine oil

b) Antifreeze

c) Sulfur from poor-quality fuel

d) Any of the above

CHAPTER QUIZ

6. Two technicians are discussing testing a catalytic converter. Technician A says that a vacuum gauge can be used and observed to see if the vacuum drops with the engine at idle for 30 seconds. Technician B says that a pressure gauge can be used to check for back pressure. Which technician is correct?a) Technician A only

CHAPTER QUIZ

6. Two technicians are discussing testing a catalytic converter. Technician A says that a vacuum gauge can be used and observed to see if the vacuum drops with the engine at idle for 30 seconds. Technician B says that a pressure gauge can be used to check for back pressure. Which technician is correct?a) Technician A only

CHAPTER QUIZ

7. A catalytic converter is being tested with an infrared pyrometer. Which is an acceptable (good converter) result?a) The inlet should be hotter than the outlet by 10%.

b) The outlet should be hotter than the inlet by 10%.

c) Both the inlet and the outlet should be the same temperature after the converter reaches operating temperature.

d) The temperature of a catalytic converter is the best test to perform to locate a restricted (clogged) unit.

CHAPTER QUIZ

7. A catalytic converter is being tested with an infrared pyrometer. Which is an acceptable (good converter) result?a) The inlet should be hotter than the outlet by 10%.

b) The outlet should be hotter than the inlet by 10%.

c) Both the inlet and the outlet should be the same temperature after the converter reaches operating temperature.

d) The temperature of a catalytic converter is the best test to perform to locate a restricted (clogged) unit.

CHAPTER QUIZ

8. Which exhaust gas reading indicates a good catalytic converter?a) O2 is zero

b) CO is zero

c) Both a and b

d) Neither a nor b

CHAPTER QUIZ

8. Which exhaust gas reading indicates a good catalytic converter?a) O2 is zero

b) CO is zero

c) Both a and b

d) Neither a nor b

CHAPTER QUIZ

9. A P0422 (catalytic converter efficiency failure) is set. What is a possible cause?a) Engine mechanical fault

b) Exhaust leak

c) Fuel contamination

d) Any of the above

CHAPTER QUIZ

9. A P0422 (catalytic converter efficiency failure) is set. What is a possible cause?a) Engine mechanical fault

b) Exhaust leak

c) Fuel contamination

d) Any of the above

CHAPTER QUIZ

10.Technician A says that the catalytic converter is warranted for eight years or 80,000 mi, whichever comes first. Technician B says that after replacing the catalytic converter, the old converter must be kept for possible inspection for 60 days. Which technician is correct?a) Technician A only

CHAPTER QUIZ

10.Technician A says that the catalytic converter is warranted for eight years or 80,000 mi, whichever comes first. Technician B says that after replacing the catalytic converter, the old converter must be kept for possible inspection for 60 days. Which technician is correct?a) Technician A only

objectives

typical catalytic converter

pearson higher education

eby james

air pump

air tube

additional air

exhaust emissions nox

exhaust manifold

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