OBJECTIVES

2. OBJECTIVES After studying Chapter 21, the reader will be able to: • Identify the component parts of the evaporative emission control system. • Discuss how the EVAP system works. • Describe how the EVAP system is tested for leaks by the PCM. • Explain how a technician can locate leaks in the EVAP system.

3. EVAPORATIVE CONTROL SYSTEMSParts and Operation • The charcoal canister used in the evaporative emission control system, which is located under the hood or underneath the vehicle, is filled with activated charcoal granules that can hold up to one-third of their own weight in fuel vapors. FIGURE 21-1 A charcoal canister can be located under the hood or underneath the vehicle.

4. EVAPORATIVE CONTROL SYSTEMSParts and Operation • Activated charcoal is an effective vapor trap because of its great surface area. • Each gram of activated charcoal has a surface area of 1,100 square meters, or more than a quarter acre. • Typical canisters hold either 300 or 625 grams of charcoal with a surface area equivalent to 80 or 165 football fields.

5. EVAPORATIVE CONTROL SYSTEMSParts and Operation FIGURE 21-2 Charcoal granules from a carbon canister.

6. EVAPORATIVE CONTROL SYSTEMSParts and Operation FIGURE 21-3 The evaporative emission control system includes all of the lines, hoses, and valves, plus the charcoal canister.

7. EVAPORATIVE CONTROL SYSTEMSVapor Purging • During engine operation, stored vapors are drawn from the canister into the engine through a hose connected to the throttle body or the air cleaner. • This “purging” process mixes HC vapors from the canister with the existing air-fuel charge.

8. EVAPORATIVE CONTROL SYSTEMSComputer-Controlled Purge • Canister purging on engines with electronic fuel management systems is regulated by the powertrain control module (PCM). • This is done by a microprocessor-controlled vacuum solenoid, along with one or more purge valves.

9. EVAPORATIVE CONTROL SYSTEMSComputer-Controlled Purge FIGURE 21-4 A typical evaporative emission control system. Note that when the computer turns on the canister purge solenoid valve, manifold vacuum draws any stored vapors from the canister into the engine. Manifold vacuum also is applied to the pressure control valve. When this valve opens, fumes from the fuel tank are drawn into the charcoal canister and eventually into the engine. When the solenoid valve is turned off (or the engine stops and there is no manifold vaccum), the pressure control valve is spring-loaded shut to keep vapors inside the fuel tank from escaping to the atmosphere.

10. EVAPORATIVE CONTROL SYSTEMSComputer-Controlled Purge • Pressure buildup is a function of: • Fuel evaporation rates (volatility) • Gas tank size (fuel surface area and volume) • Fuel level (liquid versus vapor) • Fuel slosh (driving conditions) • Temperature (ambient, in-tank, close to the tank) • Returned fuel from the rail

11. ENHANCED EVAPORATIVE CONTROL SYSTEM • Beginning in 1996 with OBD-II vehicles, manufacturers were required to install systems that were able to detect both purge flow and evaporative system leakage. • Vent Valve • Purge Valve • Service Port FIGURE 21-5 Note the label states that a maximum pressure should be applied to the service port: 1 PSI (28 inches of water).

12. LEAK DETECTION PUMP SYSTEMPurpose and Function • A leak detection pump (LDP) is a system used by Chrysler, Jeep, German vehicles, and some Mitsubishi vehicles. • This system uses positive pressure in the fuel tank to detect leaks in the system. • The leak detection pump creates the low, but positive, pressure. • A leak detection pump has the following features: • It does not use a fuel tank pressure sensor. • It pressurizes the evaporative emission control system to 7.5 inches of water (about 0.25 PSI). • This type of system does not use a vent solenoid but instead uses a spring-loaded valve in the bottom of the leak detection pump assembly, which acts as a vent for the system.

13. LEAK DETECTION PUMP SYSTEMPurpose and Function FIGURE 21-6 A typical leak detection pump assembly showing the connector.

14. LEAK DETECTION PUMP SYSTEMPurpose and Function FIGURE 21-7 A leak detection pump (LDP) used on some Chrysler vehicles to pressurize (slightly) the fuel system to check for leaks.

15. LEAK DETECTION PUMP SYSTEMPurpose and Function • Operation • Pump Period

16. ENGINE OFF, NATURAL VACUUM MONITOR • Many vehicles are monitoring the fuel tank pressure sensor after the engine has been shut off to detect a leak in the fuel evaporative system. • Gas Laws • Boyle’s Law • Charles’s law • Natural Vacuum Leak Detection • Fuel Tank Pressure Sensor FIGURE 21-8 Gas laws at work. A tank car was cleaned using steam, and then both the drain and the top vent were closed. When the air cooled inside the tank, outside air pressure caused the tank car to collapse.

17. ENGINE OFF, NATURAL VACUUM MONITOR FIGURE 21-9 Engine off, natural vacuum test monitors the pressure in the fuel tank after the engine is stopped. The pressure should rise, and then fall into a vacuum when the vent valve is closed, sealing the system.

18. ONBOARD REFUELING VAPOR RECOVERY • Purpose • The onboard refueling vapor recovery (ORVR) system was first introduced on some 1998 vehicles. • Onboard refueling vapor recovery (ORVR) is a U.S. government mandated emission control system that is designed to prevent the release of hydrocarbon (HC) emissions into the atmosphere during refueling. • Function • The primary feature of most ORVR systems is the restricted tank filler tube, which is about 1 inch (25 mm) in diameter. • This reduced size filler tube creates an aspiration effect, which tends to draw outside air into the filler tube.

19. STATE INSPECTION EVAP TESTS • In some states, a periodic inspection and test of the fuel system are mandated along with a dynamometer test. • The emissions inspection includes tests on the vehicle before and during the dynamometer test. • Before the running test, the fuel tank and cap, fuel lines, canister, and other fuel system components must be inspected and tested to ensure that they are not leaking gasoline vapors into the atmosphere.

20. DIAGNOSING THE EVAP SYSTEM • Before vehicle emissions testing began in many parts of the country, little service work was done on the evaporative emission system. • Common engine-performance problems that can be caused by a fault in this system include: • Poor fuel economy. • Poor performance.

21. LOCATING LEAKS IN THE SYSTEM • Leaks in the evaporative emission control system will cause the malfunction check gas cap indication lamp to light on some vehicles. FIGURE 21-10 Some vehicles will display a message if an evaporative control system leak is detected that could be the result of a loose gas cap.

22. LOCATING LEAKS IN THE SYSTEM FIGURE 21-11 To test for a leak, this tester was set to the 0.020-inch hole and turned on. The ball rose in the scale on the left and the red arrow was moved to that location. When testing the system for leaks, if the ball rises higher than the arrow, then the leak is larger than 0.020.If the ball does not rise to the level of the arrow, the leak is smaller than 0.020 inch.

23. LOCATING LEAKS IN THE SYSTEMSmoke Machine Testing • The most efficient method of leak detection is to introduce smoke under low pressure from a machine specifically designed for this purpose. FIGURE 21-12 This unit is applying smoke to the fuel tank through an adapter. The leak was easily found to be in the gas cap seal.

24. EVAPORATIVE SYSTEM MONITOR • The EVAP system monitor tests for purge volume and leaks. • Most applications purge the charcoal canister by venting the vapors into the intake manifold during cruise. • To do this, the PCM typically opens a solenoid-operated purge valve installed in the purge line leading to the intake manifold.

25. EVAPORATIVE SYSTEM MONITOR FIGURE 21-13 The fuel tank pressure sensor (black unit with three wires) looks like a MAP sensor and is usually located on top of the fuel pump module (white unit).

26. EVAPORATIVE SYSTEM MONITOREngine Off Natural Vacuum • System integrity (leakage) can also be checked after the engine is shut off. • The theory is that a warm evaporative system will cool down after the engine is shut off and the vehicle is stable. • A slight vacuum will be created in the gas tank during this cool-down period. • If a specific level of vacuum is reached and maintained, the system is said to have integrity (no leakage).

27. EVAPORATIVE SYSTEM MONITOREngine Off Natural Vacuum FIGURE 21-14 In the Ford EVAP monitor test, the purge valve is opened with the vent valve closed, lowering the pressure in the fuel tank. At about 14 seconds, the vacuum in the tank has reached its target and the valve is closed. The PCM monitors how quickly the vacuum is lost.

28. TYPICAL EVAP MONITOR • The PCM will run the EVAP monitor when the following enable criteria are met. • Typical enable criteria include: • Cold start • BARO greater than 70 kPa (20.7 in. Hg or 10.2 PSI) • IAT between 39°F and 86°F at engine start-up • ECT between 39°F and 86°F at engine start-up • ECT and IAT within 39°F of each other at engine start-up • Fuel level within 15% to 85% • TP sensor between 9% and 35%

29. TYPICAL EVAP MONITORRunning the EVAP Monitor • Four tests are performed during a typical GM EVAP monitor. • A DTC is assigned to each test. • Weak Vacuum Test (P0440—large leak). • Small Leak Test (P0442—small leak). • Excess Vacuum Test (P0446). • Purge Solenoid Leak Test (P1442).

30. ALWAYS TIGHTEN THE CAP CORRECTLY FIGURE 21-15 This Toyota cap has a warning: the check engine light will come on if not tightened until one click.

31. KEEP THE FUEL TANK PROPERLY FILLED FIGURE 21-16 The fuel level must be above 15% and below 85% before the EVAP monitor will run on most vehicles.

32. EVAP SYSTEM-RELATED DIAGNOSTIC TROUBLE CODES (DTC)

33. SUMMARY • A canister filled with charcoal granules is used to store gasoline vapors until they are purged. When purge occurs, the vapors are drawn into the intake manifold and enter the engine where they are burned in the cylinder. • The pressure and vacuum in the evaporative emission control system is very low and measured in inches of water. Twenty-eight inches of water is equal to 1 pound per square inch (PSI). • Enhanced evaporative emission control systems include a fuel tank pressure sensor used to detect leaks in the system.

34. SUMMARY • The purge valve is normally closed and electrically open. The vent valve is normally open and electrically open. • A leak detection pump system is used on some vehicles to pressurize the system and check for leaks. • Engine off, natural vacuum (EONV) is used on some vehicles to detect leaks in the system. • Onboard refueling vapor recovery (ORVR) was first introduced on some 1998 vehicles. • Nitrogen and smoke are used to locate leaks in the EVAP system.

35. REVIEW QUESTIONS • Why does the carbon canister get hot when the vehicle is being refueled? • What is the relationship between inches of water and pounds per square inch? • Where is the service port located in the system? • What is unique about a system that is equipped with onboard refueling vapor recovery (ORVR)?

36. CHAPTER QUIZ • Technician A says that the purge valve is normally closed. Technician B says that the vent valve is normally closed. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

37. CHAPTER QUIZ • Technician A says that the purge valve is normally closed. Technician B says that the vent valve is normally closed. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

38. CHAPTER QUIZ 2. Twenty-eight inches of water vacuum is equal to how many inches of Mercury of vacuum? • 14.7 • 2 • 0.8 • 0.16

39. CHAPTER QUIZ 2. Twenty-eight inches of water vacuum is equal to how many inches of Mercury of vacuum? • 14.7 • 2 • 0.8 • 0.16

40. CHAPTER QUIZ 3. A service port, if equipped, is generally located between the purge valve and the charcoal canister. Technician A says that the Schrader valve uses left-hand threads. Technician B says that the maximum pressure allowed to be applied to the service port is 1 PSI. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

41. CHAPTER QUIZ 3. A service port, if equipped, is generally located between the purge valve and the charcoal canister. Technician A says that the Schrader valve uses left-hand threads. Technician B says that the maximum pressure allowed to be applied to the service port is 1 PSI. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

42. CHAPTER QUIZ 4. A typical leak detection pump applies how much pressure to the fuel system? • 0.25 PSI • 1.00 PSI • 7.50 PSI • 14 PSI

43. CHAPTER QUIZ 4. A typical leak detection pump applies how much pressure to the fuel system? • 0.25 PSI • 1.00 PSI • 7.50 PSI • 14 PSI

44. CHAPTER QUIZ 5. When the engine is shut off, what normally happens to the pressure inside the gas tank if the vent and purge valve are both closed? • The pressure rises, and then falls when the temperature drops. • The pressure drops, and then rises as the vapors increase in the tank. • The pressure remains the same and does not change until the temperature drops, and then the pressure drops. • In a sealed system, the pressure is constant regardless of temperature.

45. CHAPTER QUIZ 5. When the engine is shut off, what normally happens to the pressure inside the gas tank if the vent and purge valve are both closed? • The pressure rises, and then falls when the temperature drops. • The pressure drops, and then rises as the vapors increase in the tank. • The pressure remains the same and does not change until the temperature drops, and then the pressure drops. • In a sealed system, the pressure is constant regardless of temperature.

46. CHAPTER QUIZ 6. What is unique about a fuel system that is equipped with an onboard refueling vapor recovery (ORVR) system? • It uses two charcoal canisters. • It uses a restricted tank filler tube. • It does not use a vent valve. • Both a and c

47. CHAPTER QUIZ 6. What is unique about a fuel system that is equipped with an onboard refueling vapor recovery (ORVR) system? • It uses two charcoal canisters. • It uses a restricted tank filler tube. • It does not use a vent valve. • Both a and c

48. CHAPTER QUIZ 7. A small leak is being verified using a tester. The arrow on the flow gauge is set to the 0.020 inch rate of leakage. During the test, the ball rises above the arrow. Technician A says that the test verifies that a leak larger than 0.020 inch exists. Technician B says that because the ball rose above the arrow, this indicates that the leak is smaller than 0.020. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

49. CHAPTER QUIZ 7. A small leak is being verified using a tester. The arrow on the flow gauge is set to the 0.020 inch rate of leakage. During the test, the ball rises above the arrow. Technician A says that the test verifies that a leak larger than 0.020 inch exists. Technician B says that because the ball rose above the arrow, this indicates that the leak is smaller than 0.020. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

50. CHAPTER QUIZ 8. The evaporative emission control monitor will not run unless the fuel is at what level? • Full or almost full • 40% to 60% • 15% to 85% • 5% to 90%