Emission Control Systems: Description and Operation

Engine Emission Control - 4.6L, 5.4L and 6.8L

NOTE: Do not permanently remove or render inoperative any part of the vehicle emission control system including related hardware. Failure to comply may violate applicable state and federal law.

NOTE: The vehicle emission vacuum routing diagrams are contained in the Description and Operation subsection of the Evaporative Emissions system.

The engine emission control system consists of the following:

- PCV system

- EGR system (4.6L [2V] only)

EGR System

The EGR system:

- returns a small amount of exhaust gas into the engine for recombustion.

- reduces the overall combustion temperature and provides a significant reduction of Nitrogen Oxides (NOx).

The EGR system module:

- is electronically controlled by the PCM.

- is connected to the exhaust manifold by the EGR system module-to-exhaust manifold tube.

- controls recirculated exhaust gas flow to the intake manifold.

- monitors the flow of recirculated exhaust gases through the EGR valve-to-exhaust manifold tube.

- returns a signal to the PCM.

The amount of recirculated exhaust gas depends on:

- engine rpm.

- intake manifold vacuum.

- exhaust back pressure.

- engine coolant temperature.

- throttle position.

PCV System

The PCV system:

- uses intake manifold vacuum to ventilate blow-by fumes from the crankcase.

- returns the fumes to the intake manifold for combustion.

The PCV valve:

- varies the amount of blow-by gases returned to the intake manifold based on available engine vacuum.