Engine Emission Control

Engine Emission Control

NOTICE: 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 includes the:

- EGR valve.
- EGR valve-to-intake manifold tube (2.3L).
- exhaust manifold-to-EGR valve tube (4.0L SOHC).
- EGR vacuum regulator solenoid.
- PCV valve.


EGR

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 Nitrogen Oxides (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 SOHC Engine

The 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 PCM.

The amount of recirculated exhaust gas depends upon:

- engine rpm.
- intake manifold vacuum.
- exhaust backpressure.
- Engine Coolant Temperature (ECT).
- throttle position.


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 coolant-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.


Evaporative Emission (EVAP), EGR and PCV Vacuum Routing

2.3L Engine









4.0L SOHC Engine