OBJECTIVES

2. OBJECTIVES After studying Chapter 28, the reader will be able to: • Prepare for the ASE Engine Performance (A8) certification test content area “D” (Emission Control Systems). • Describe the purpose and function of the positive crankcase ventilation and the air-injection reaction system. • Discuss how the PCV and SAI systems are tested under OBD-II regulations. • Explain methods for diagnosing and testing faults in the PCV and SAI systems.

3. BACKGROUND • The process of combustion produces power in an internal-combustion engine. • Under perfect conditions, combustion would completely consume the air-fuel mixture, leaving only harmless by-products, such as water vapor (H2O) and carbon dioxide (CO2). • Combustion of the air-fuel mixture is never perfect, however, and at best is incomplete. • By-products other than H2O and CO2 remain after the combustion process and go out the tailpipe. • These by-products of incomplete combustion include carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NOX).

4. CRANKCASE VENTILATION • The problem of crankcase ventilation has existed since the beginning of the automobile because no piston ring, new or old, can provide a perfect seal between the piston and the cylinder wall. • Positive crankcase ventilation (PCV) systems were developed to ventilate the crankcase an recirculate the vapors to the engine’s induction system so they can be burned in the cylinders.

5. CRANKCASE VENTILATIONClosed PCV Systems FIGURE 28-1 A PCV system includes a hose from the air cleaner assembly so that filtered air can be drawn into the crankcase. This filtered air is then drawn by engine vacuum through the PCV valve and into the intake manifold where the crankcase fumes are burned in the cylinder. The PCV valve controls and limits this flow of air and fumes into the engine and the valve closes in the event of a backfire to prevent flames from entering the crankcase area.

6. CRANKCASE VENTILATIONClosed PCV Systems FIGURE 28-2 A dirty PCV vent filter inside the air cleaner housing. The air enters the crankcase through this filter and then is drawn into the engine through the PCV valve.

7. PCV VALVES • The PCV valve in most systems is a one-way valve containing a spring-operated plunger that controls valve flow rate. FIGURE 28-3 Spring force, crankcase pressure, and intake manifold vacuum work together to regulate the flow rate through the PCV valve.

8. PCV VALVES FIGURE 28-4 Air flows through the PCV valve during idle, cruising, and light-load conditions.

9. PCV VALVES FIGURE 28-5 Air flows through the PCV valve during acceleration and when the engine is under a heavy load.

10. PCV VALVES FIGURE 28-6 PCV valve operation in the event of a backfire.

11. ORIFICE-CONTROLLED SYSTEMS • While most orifice flow control systems work the same as a PCV valve system, they may not use fresh air scavenging of the crankcase. • Crankcase vapors are drawn into the intake manifold in calibrated amounts depending on manifold pressure and the orifice size. • If vapor availability is low, as during idle, air is drawn in with the vapors. • During off-idle operation, excess vapors are sent to the air cleaner; as crankcase pressure increases oil, the gases backup.

12. POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM DIAGNOSIS • When intake air flows freely, the PCV system functions properly, as long as the PCV valve or orifice is not clogged. • Modern engine design includes the air and vapor flow as a calibrated part of the air-fuel mixture. FIGURE 28-7 A visual inspection found this deteriorated PCV vacuum hose.

13. POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM DIAGNOSIS • PCV System Performance Check • A properly operating positive crankcase ventilation system should be able to draw vapors from the crankcase and into the intake manifold. • If the pipes, hoses, and PCV valve itself are not restricted, vacuum is applied to the crankcase. • A slight vacuum is created in the crankcase (usually less than 1 in. Hg if measured at the dipstick) and is also applied to other areas of the engine. • There are several methods that can be used to test a PCV system. • The Rattle Test • The 3 x 5 Card Test • The Snap-Back Test • Crankcase Vacuum Test

14. POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM DIAGNOSIS FIGURE 28-8 A typical PCV valve. A defective or clogged PCV valve or hose can cause a rough idle or stalling problem. Because the air flow through the PCV valve accounts for about 20% of the air needed by the engine at idle, use of the incorrect valve for an application could have a severe effect on idle quality.

15. POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM DIAGNOSIS FIGURE 28-9 A typical PCV valve installed in a rubber grommet in the valve cover.

16. POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM DIAGNOSIS FIGURE 28-10 A water manometer being used to check for a slight vacuum when testing at the oil dipstick tube.

17. PCV MONITOR • All vehicles must be checked for proper operation of the PCV system starting with 2004 and newer vehicles. • The PCV monitor will fail if the PCM detects an opening between the crankcase and the PCV valve or between the PCV valve and the intake manifold

18. PCV-RELATED DIAGNOSTIC TROUBLE CODE

19. SECONDARY AIR INJECTION (SAI) SYSTEM • An air pump provides the air necessary for the oxidizing process inside the catalytic converter. FIGURE 28-11 A typical belt-driven air pump. Air enters through the revolving fins. These fins act as a moving air filter because dirt is heavier than air and therefore the dirt in the air is deflected off the fins at the same time the air is drawn into the pump.

20. SECONDARY AIR INJECTION (SAI) SYSTEMAir Switching Valves FIGURE 28-12 (a) When the engine is cold and before the oxygen sensor is hot enough to reach closed loop, the air flow is directed to the exhaust manifold(s) through one-way check valve(s). These valves keep exhaust gases from entering the switching solenoids and the air pump itself. (b) When the engine achieves closed loop, the air flows from the pump, is directed to the catalytic converter, and then moves through a check valve.

21. AIR DISTRIBUTION MANIFOLDS AND NOZZLES • Air is delivered to the exhaust system in one of two ways: • An external air manifold, or manifolds, distributes the air through injection tubes with stainless steel nozzles. The nozzles are threaded into the cylinder heads or exhaust manifolds close to each exhaust valve. • An internal air manifold distributes the air to the exhaust ports near each exhaust valve through passages cast in the cylinder head or the exhaust manifold.

22. AIR DISTRIBUTION MANIFOLDS AND NOZZLES • Three basic types of air pumps are the belt-driven air pump, the pulse air-driven air pump, and the electric motor-driven air pump. • Exhaust Check Valves • Belt-Driven Air Pumps • Electric Motor-Driven Air Pumps • Pulse Air-Driven Devices

23. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-13 An AIR exhaust check valve between the rubber air hose and the metal discharge tubes.

24. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-14 A typical electric motor-driven AIR pump. This unit is on a Chevrolet Corvette and only works when the engine is cold.

25. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-15 Exhaust check valves in the AIR system allow air to flow in only one direction.

26. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-16 A typical belt-driven air pump used on an older model Chevrolet Corvette.

27. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-17 The air pump supplies air to the exhaust port of each cylinder. Unburned HCs are oxidized into CO2 and H2O and CO is converted to CO2.

28. AIR DISTRIBUTION MANIFOLDS AND NOZZLES FIGURE 28-18 Cutaway of a pulse air-driven air device used on many older engines to deliver air to the exhaust port through the use of the exhaust pulses acting on a series of one-way check valves. Air from the air cleaner assembly moves through the system and into the exhaust port where the additional air helps reduce HC and CO exhaust emissions.

29. AIR-PUMP SYSTEM DIAGNOSIS • The air-pump system should be inspected if an exhaust emissions test failure occurs. • Visual Inspection • Four-Gas Exhaust Analysis

30. AIR-RELATED DIAGNOSTIC TROUBLE CODE

31. SUMMARY • Positive crankcase ventilation (PCV) systems use a valve or a fixed orifice to control the fumes from the crankcase back into the intake system. • A PCV valve regulates the flow of fumes depending on engine vacuum and seals the crankcase vent in the event of a backfire. • As much as 30% of the air needed by the engine at idle speed flows through the PCV system.

32. SUMMARY • PCV tests include the rattle test, card test, snap-back test, and crankcase vacuum test. • The AIR system forces air at low pressure into the exhaust to reduce CO and HC exhaust emissions. • Exhaust check valves are used between the AIR pump and the exhaust manifold to prevent exhaust gases from flowing into, and causing damage to, the AIR pump and valves.

33. REVIEW QUESTIONS • What exhaust emissions do the PCV valve and AIR system control? • How does a PCV valve work? • What does the abbreviation PCV mean? • What does the abbreviation AIR mean?

34. CHAPTER QUIZ • The PCV system controls which exhaust emission(s)? • HC • CO • NOX • Both HC and CO

35. CHAPTER QUIZ • The PCV system controls which exhaust emission(s)? • HC • CO • NOX • Both HC and CO

36. CHAPTER QUIZ 2. How much of the air needed by the engine flows through the PCV system when the engine is at idle speed? • 1% to 3% • 5% to 10% • 10% to 20% • Up to 30%

37. CHAPTER QUIZ 2. How much of the air needed by the engine flows through the PCV system when the engine is at idle speed? • 1% to 3% • 5% to 10% • 10% to 20% • Up to 30%

38. CHAPTER QUIZ 3. Technician A says that if the PCV system were defective or clogged, the engine could idle rough. Technician B says that the engine may stall. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

39. CHAPTER QUIZ 3. Technician A says that if the PCV system were defective or clogged, the engine could idle rough. Technician B says that the engine may stall. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

40. CHAPTER QUIZ 4. Technician A says that if a PCV valve rattles, then it is okay and does not need to be replaced. Technician B says that if a PCV valve does not rattle, it should be replaced. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

41. CHAPTER QUIZ 4. Technician A says that if a PCV valve rattles, then it is okay and does not need to be replaced. Technician B says that if a PCV valve does not rattle, it should be replaced. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

42. CHAPTER QUIZ 5. Technician A says that the PCV system should create a slight pressure in the crankcase at idle. Technician B says that the PCV system should create a slight vacuum in the crankcase at 2500 RPM. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

43. CHAPTER QUIZ 5. Technician A says that the PCV system should create a slight pressure in the crankcase at idle. Technician B says that the PCV system should create a slight vacuum in the crankcase at 2500 RPM. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

44. CHAPTER QUIZ 6. The SAI system is used to reduce which exhaust emission(s)? • HC • CO • NOX • Both HC and CO

45. CHAPTER QUIZ 6. The SAI system is used to reduce which exhaust emission(s)? • HC • CO • NOX • Both HC and CO

46. CHAPTER QUIZ 7. Two technicians are discussing exhaust check valves used in AIR systems. Technician A says that they are used to prevent the output from the AIR pump from entering the intake manifold. Technician B says the check valves are used to keep the exhaust from entering the AIR pump. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

47. CHAPTER QUIZ 7. Two technicians are discussing exhaust check valves used in AIR systems. Technician A says that they are used to prevent the output from the AIR pump from entering the intake manifold. Technician B says the check valves are used to keep the exhaust from entering the AIR pump. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

48. CHAPTER QUIZ 8. Where is the output of the AIR pump directed when the engine is cold? • Exhaust manifold • Catalytic converter • Air cleaner assembly • To the atmosphere

49. CHAPTER QUIZ 8. Where is the output of the AIR pump directed when the engine is cold? • Exhaust manifold • Catalytic converter • Air cleaner assembly • To the atmosphere

50. CHAPTER QUIZ 9. The switching valves on the AIR pump have failed several times. Technician A says that a defective exhaust check valve could be the cause. Technician B says that a restricted exhaust system could be the cause. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B