Engine Emission Control

ENGINE EMISSION CONTROL

CAUTION: Do not remove any part of the engine emission control system. Operating the engine without the engine emission control system intact will reduce fuel economy and engine ventilation. This will weaken engine performance and shorten engine life.

The engine emission control system consists of the:
- positive crankcase ventilation (PCV) system.
- exhaust gas recirculation (EGR) system (2.3L and 4.0L engines only).

Exhaust Gas Recirculation
The EGR system returns a small amount of exhaust gas into the intake manifold. This reduces the overall combustion temperature. Cooler combustion temperatures provide a significant reduction of the oxides of nitrogen (NOx) in the exhaust emissions.

2.3L Engine
The 2.3L engine incorporates a stepper motor-controlled EGR valve which receives its signal from the PCM. Engine coolant is used to cool the EGR valve. The EGR valve and stepper motor are serviced as an assembly.

4.0L Engine
The powertrain control module (PCM) controls the EGR vacuum regulator solenoid. The EGR vacuum regulator solenoid controls the vacuum to the EGR valve. When the EGR valve opens, exhaust gas flows to the intake manifold to be returned to the combustion cycle. The differential pressure feedback EGR system monitors the flow and returns a signal to the powertrain control module (PCM).

The amount of recirculated exhaust gas depends upon:
- engine rpm.
- intake manifold vacuum.
- exhaust backpressure.
- engine coolant temperature.
- throttle position.

Exhaust Emission Control System
The vehicle emission control information (VECI) decal is located on the upper radiator support and shows:
- components of the emission control system.
- the correct vacuum hose routing.
- the color stripe of the vacuum hoses.

Positive Crankcase Ventilation (PCV) System
The PCV system uses intake manifold vacuum to ventilate blow-by fumes from the crankcase and return the fumes to the intake manifold for combustion. The 2.3L engine does this through a water-heated fitting. The PCV valve varies the amount of blow-by gasses returned to the intake manifold based on available engine vacuum. The PCV valve also prevents the entry of combustion backfiring into the crankcase.