Emission Control Systems: Description and Operation

Positive Crankcase Ventilation (PCV) System

CAUTION: Do not remove the PCV system from the engine. Operating engine without the PCV system will reduce both fuel economy and engine ventilation. This will weaken engine performance and shorten engine life.

The Positive Crankcase Ventilation (PCV) system cycles crankcase gases back through the engine where they are burned. The positive crankcase ventilation (PCV) valve:
^ regulates the amount of ventilating air and blow-by fuel vapor to the intake manifold.
^ prevents backfire from traveling into the crankcase.
^ is mounted in a vertical position.

Exhaust Gas Recirculation (EGR) System
The Exhaust Gas Recirculation (EGR) system is designed to:
^ reintroduce exhaust gas into the combustion cycle.
^ lower combustion temperatures.
^ reduce the formation of nitrous oxide.

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by the following:
^ engine rpm
^ engine vacuum
^ exhaust system backpressure
^ engine coolant temperature
^ throttle position

The exhaust gas recirculation (EGR) valve is vacuum actuated.

The differential pressure feedback EGR system:
^ monitors EGR flow rate by the pressure drop across the metering orifice.
^ uses a differential pressure feedback EGR sensor as the feedback device.
^ controls pressure that is varied by the valve movement using vacuum output of the EGR vacuum regulator solenoid.
^ uses the EGR valve only as a pressure regulator, rather than a flow metering device.
^ allows for a more accurate assessment of EGR flow requirements.
^ sends the PCM a signal indicating exhaust pressure.

Exhaust Emission Control System

Vehicle Emission Control Information Decal
Vacuum hoses on the engine use a color stripe to aid in hose routing checks. The stripe will usually be the same color as on the vehicle emission control information decal, but the correct vacuum hose routing must be verified by using the correct component connections shown on the decal.