Chapter 26

CHAPTER 26

Exhaust Gas Recirculation Systems

Automotive Fuel and Emissions Control Systems 3/e By James D. Halderman

Copyright © 2012, 2009, 2006 Pearson Education, Inc.,Upper Saddle River, NJ 07458 • All rights reserved.2

After studying Chapter 26, the reader will be able to:

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

2. Describe the purpose and function of the exhaust gas recirculation system.

3. Discuss how the exhaust gas recirculation system is tested under OBD-II regulations.

4. Explain methods for diagnosing and testing for faults in the exhaust gas recirculation system.

OBJECTIVES



KEY TERMS

• Delta pressure feedback EGR (DPFE) sensor

• Detonation • Digital EGR valve • EGR valve position (EVP)

sensor • Electronic vacuum

regulator valve (EVRV)

• Exhaust gas recirculation (EGR)

• Inert • Linear EGR valve • Nitrogen oxides (NO x )• Pressure feedback EGR

(PFE) sensor



EXHAUST GAS RECIRCULATION SYSTEMS

• Exhaust gas recirculation (EGR) is an emission control system that lowers the amount of nitrogen oxides (NOx) formed during combustion.

• In the presence of sunlight, NOx reacts with hydrocarbons in the atmosphere to form ozone (O3) or photochemical smog, an air pollutant.




• NOX FORMATION

• CONTROLLING NOX

• EGR SYSTEM OPERATION• EGR BENEFITS• POSITIVE AND NEGATIVE BACK PRESSURE

EGR VALVES• COMPUTER-CONTROLLED EGR SYSTEMS• EGR VALVE POSITION SENSORS• DIGITAL EGR VALVES• LINEAR EGR




FIGURE 26–1 Nitrogen oxides (NO x ) create a red-brown haze that often hangs over major cities.




FIGURE 26–2 When the EGR valve opens, the exhaust gases flow through the valve and into passages in the intake manifold.




FIGURE 26–3 Back pressure in the exhaust system is used to close the control valve, allowing engine vacuum to open the EGR valve.




FIGURE 26–4 Typical vacuum-operated EGR valve. The operation of the valve is controlled by the PCM by pulsing the EGR control solenoid on and off.




FIGURE 26–5 An EGR valve position sensor on top of an EGR valve.




FIGURE 26–6 Digital EGR valve as used on some older General Motors engines.




FIGURE 26–7 A General Motors linear EGR valve.



Find the Root Cause

• Excessive back pressure, such as that caused by a partially clogged exhaust system, could cause the plastic sensors on the EGR valve to melt. Always check for a restricted exhaust whenever replacing a failed EGR valve sensor.



OBD-II EGR MONITORING STRATEGIES

• PURPOSE AND FUNCTION• MONITORING STRATEGIES

FIGURE 26–9 A typical Ford DPFE sensor and related components.



OBD-II EGR MONITORING STRATEGIES

FIGURE 26–10 An OBD-II active test. The PCM opens the EGR valve and then monitors the MAP sensor and/or engine speed (RPM) to verify that it meets acceptable values.



DIAGNOSING A DEFECTIVE EGR SYSTEM

• SYMPTOMS• If the EGR valve is not opening or the flow of the exhaust gas

is restricted, then the following symptoms are likely:• Detonation (spark knock or ping) during acceleration or during

cruise (steady-speed driving)• Excessive oxides of nitrogen (NO x ) exhaust emissions

• If the EGR valve is stuck open or partially open, then the following symptoms are likely:

• Rough idle or frequent stalling• Poor performance/low power, especially at low engine speed

• EGR TESTING PROCEDURES



Watch Out for Carbon Balls!

• EGR valves can get stuck partially open by a chunk of carbon, and the valve or solenoid will test as defective. When the valve (or solenoid) is removed, small chunks or balls of carbon often fall into the exhaust manifold passage. When the replacement valve is installed, the carbon balls can be drawn into the new valve again, causing the engine to idle roughly or stall.

• To help prevent this problem, start the engine with the EGR valve or solenoid removed. Any balls or chunks of carbon will be blown out of the passage by the exhaust. Stop the engine and install the replacement EGR valve or solenoid.



The Blazer Story

• The owner of a Chevrolet Blazer equipped with a 4.3-L, V-6 engine complained that the engine would stumble and hesitate at times. Everything seemed to be functioning correctly, except that the service technician discovered a weak vacuum going to the EGR valve at idle. This vehicle was equipped with an EGR valve-control solenoid, called an electronic vacuum regulator valve (EVRV) by General Motors Corporation. The PCM pulses the solenoid to control the vacuum that regulates the operation of the EGR valve. The technician checked the service manual for details on the workings of the system. The technician discovered that vacuum should be present at the EGR valve only when the gear selector indicates a drive gear (drive, low, reverse). Because the technician discovered the vacuum at the solenoid to be leaking, the solenoid was obviously defective and required replacement. After replacement of the solenoid (EVRV), the hesitation problem was solved.



The Snake Trick

• The EGR passages on many intake manifolds become clogged with carbon, which reduces the flow of exhaust and the amount of exhaust gases in the cylinders. This reduction can cause spark knock (detonation) and increased emissions of oxides of nitrogen (NOx) (especially important in areas with enhanced exhaust emissions testing).

• To quickly and easily remove carbon from exhaust passages, cut an approximately 1-foot (30-cm) length from stranded wire, such as garage door guide wire or an old speedometer cable. Flare the end and place the end of the wire into the passage. Set your drill on reverse and turn it on, and the wire will pull its way through the passage, cleaning the carbon as it goes, just like a snake in a drainpipe. Some vehicles, such as Hondas, require that plugs be drilled out to gain access to the EGR passages.



The Snake Trick

FIGURE 26–11 Removing the EGR passage plugs from the intake manifold on a Honda.



SUMMARY

1. Oxides of nitrogen (NOx) are formed inside the combustion chamber because of heat exceeding 2,500°F (1,370°C).

2. Recirculating 6% to 10% inert exhaust gases back into the intake system reduces peak temperature inside the combustion chamber and reduces NO x exhaust emissions.

3. EGR is usually not needed during cold engine operation, at idle speeds or during wide-open throttle conditions.

4. Vacuum-operated EGR valves are usually exhaust back pressure controlled to help match EGR flow into the intake with the load on the engine.



SUMMARY

5. Many EGR systems use a feedback potentiometer to signal the PCM about the position of the EGR valve pintle.

6. Some EGR valves are solenoids or pulse-width modulated pintles.

7. OBD-II requires that the flow rate be tested, which can be achieved by opening the EGR valve and observing the reaction of the MAP sensor.



REVIEW QUESTIONS

1. What causes the formation of oxides of nitrogen?

2. How does the use of exhaust gas reduce NO x exhaust emission?

3. How does the DPFE sensor work?

4. How does the PCM determine that the exhaust flow through the EGR system meets OBD-II regulations?



CHAPTER QUIZ

1. What causes the nitrogen and the oxygen in the air to combine and form NOx?

a. Sunlight

b. Any spark will cause this to occur

c. Heat above 2,500°F (1,370°C)

d. Chemical reaction in the catalytic converter



CHAPTER QUIZ

2. Exhaust gas recirculation (EGR) is generally not needed under all the following conditions except ______________ .

a. Idle speed

b. Cold engine

c. Cruise speed

d. Wide-open throttle (WOT)



CHAPTER QUIZ

3. Technician A says that a low-restriction exhaust system could prevent a back pressure-type vacuum-controlled EGR valve from opening correctly. Technician B says restricted exhaust can cause the EGR valve position sensor to fail. 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

4. EGR is used to control which exhaust emission?a. Unburned hydrocarbons (HC)

b. Oxides of nitrogen (NOx)

c. Carbon monoxide (CO)

d. Both NOx and CO



CHAPTER QUIZ

5. A typical EGR pintle-position sensor is what type of sensor?

a. Rheostat

b. Piezoelectric

c. Wheatstone bridge

d. Potentiometer



CHAPTER QUIZ

6. OBD-II regulations require that the EGR system be tested. Technician A says that the PCM can monitor the commanded position of the EGR valve to determine if it is functioning correctly. Technician B says that the PCM can open the EGR valve and monitor for a change in the MAP sensor or oxygen sensor reading to detect if the system is functioning correctly. Which technician is correct?a. Technician A onlyb. Technician B onlyc. Both Technicians A and Bd. Neither Technician A nor B



CHAPTER QUIZ

7. Two technicians are discussing clogged EGR passages. Technician A says clogged EGR passages can cause excessive NOx exhaust emission. Technician B says that clogged EGR passages can cause the engine to ping (spark knock or detonation). Which technician is correct?







CHAPTER QUIZ

8. An EGR valve that is partially stuck open would most likely cause what condition?

a. Rough idle/stalling

b. Excessive NOx exhaust emissions

c. Ping (spark knock or detonation)

d. Missing at highway speed



CHAPTER QUIZ

9. When testing an EGR system for proper operation using a vacuum gauge, how much should the vacuum drop when the EGR is commanded on by a scan tool?

a. 1 to 2 in. Hg

b. 3 to 5 in. Hg

c. 6 to 8 in. Hg

d. 8 to 10 in. Hg



CHAPTER QUIZ

10.A P0401 DTC (exhaust gas recirculation flow insufficient) is being discussed. Technician A says that a defective EGR valve could be the cause. Technician B says that clogged EGR passages could be the cause. Which technician is correct?





Chapter 26

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