1. PCV and EVAP Emission Control Systems
Chapter Lesson 2

2. Positive Crankcase Ventilation (PCV)
Uses engine vacuum to draw blowby gases from the crankcase into the intake manifold for burning
Blowby is caused by leakage past the piston rings
Reduces HC, CO, and particulates

3. PCV System

4. PCV Valve Controls flow through the system
Located in the valve cover, intake manifold, or the side of the engine block
Varies flow for idle, cruise, acceleration, wide open throttle, and engine-off conditions

5. Air-Oil Separator May be used instead of a PCV valve
Makes oil vapors condense and flow back into the oil pan

6. Evaporative Emissions Control Systems (EVAP)
Prevent fuel vapors from entering the atmosphere
Before emission controls were used, vehicles vented vapors from their fuel tanks and carburetor bowls to the atmosphere

7. Evaporative System

8. Components Non-vented fuel cap Air dome or liquid-vapor separator
Rollover valve
Charcoal canister
Purge valve

9. Non-Vented Fuel Cap Prevents fuel vapors from entering the atmosphere
The pressure and vacuum relief valve will vent if tank pressure or vacuum levels get excessively high

10. Air Dome A hump formed in the top of the fuel tank
Allows for fuel expansion without spillage
Provides about 10% air space to allow for fuel heating and expansion

11. Rollover Valve
Keeps liquid fuel from entering the vent line if the vehicle rolls over
A metal ball or plunger valve blocks the vent line when the valve is turned over

12. Stores fuel vapors when the engine is not running
Charcoal Canister
Stores fuel vapors when the engine is not running

13. Purge Valve Controls the flow of vapors
Operated electrically or by vacuum
Located on top of the canister or in the purge line
Generally allows flow when the engine is operating above idle and at operating temperature

14. Engine off Operation
Fuel tank vapors are routed to the charcoal canister for storage
Activated charcoal absorbs and holds the vapors

15. Engine Running Operation
Above idle, ported manifold vacuum causes the purge valve to open
Gases flow through the purge line
Fresh air is drawn into the canister
Incoming air carries gases to the intake manifold for burning

16. This system uses a vacuum- controlled purge valve
Evaporative System
This system uses a vacuum- controlled purge valve

17. This system uses an electronically-controlled purge solenoid
Evaporative System
This system uses an electronically-controlled purge solenoid

18. Enhanced System Provides better control
Monitors the condition of the fuel system

19. Enhanced System

20. Components Fuel tank pressure sensor Canister vent solenoid
Control module
Service port

21. Fuel Tank Pressure Sensor
Monitors fuel tank pressure
Sends a pressure signal to the control module

22. Canister Vent Solenoid
Electrically operated vacuum valve replaces the fresh air vent used on older canisters
Closed by the control module to perform diagnostic tests on the evaporative system

23. Service Port
Used on many enhanced evaporative emission control systems
Fitting allows the connection of service tools for testing and cleaning

24. Enhanced System Operation
Uses a normally closed, pulse-width modulated purge solenoid
When energized, the purge solenoid allows vapors to flow to the intake manifold
The canister vent solenoid is normally open, allowing fresh air into the canister, and may be closed by the control module during diagnostics