Emission Control Systems: Description and Operation

Emission Systems:

In order to reduce exhaust emissions, these vehicles utilize an evaporative emission control system, exhaust gas recirculation system, air injection system, positive crankcase ventilation system and catalytic converters.

AIR INJECTION SYSTEM (AIR)
To reduce carbon monoxide and hydrocarbon emissions during engine warm-up, this system delivers air to the exhaust manifolds to aid oxidation. The air pump is equipped with an ECM controlled electric clutch, permitting the pump to be turned "ON" or "OFF" under specified operating conditions.

EVAPORATIVE EMISSION CONTROL SYSTEM (EVAP)
When the engine is not running, the evaporative emission control system stores fuel tank vapors in a canister containing activated charcoal. Vapors stored in the canister are drawn into the engine and burned during specified operating conditions.

EXHAUST GAS RECIRCULATION SYSTEM (EGR)
The exhaust gas recirculation system introduces regulated amounts of exhaust gas into the intake manifold to reduce NOx in exhaust gas by lowering combustion chamber temperatures. The system is ECM controlled and operates depending on engine load, engine speed, coolant temperature, etc.

POSITIVE CRANKCASE VENTILATION SYSTEM (PCV)
This system prevents crankcase fumes from being vented to atmosphere. It is designed to maintain a vacuum in the crankcase and pipe fumes into the intake manifold through a part throttle control orifice and the engine air intake system.

CATALYTIC CONVERTERS (CAT)
Catalytic converters reduce emissions of CO and HC. The 4.0L engine utilizes ceramic monolith converters mounted in the exhaust system. One of these (downpipe converter) is close to the engine and pair are under the vehicle. Platinum and rhodium are commonly used as catalysts to stimulate reactions which reduce exhaust gases to carbon dioxide and water vapor.