EMISSION APPLICATIONS
Several systems are used to control emissions. System usage depends on model, engine and transmission combinations. Each system is designed to control a particular vehicle emission. In addition, specially calibrated carburetors, distributors and modified combustion chambers are used with these systems.
AIR INJECTION
Air injection system consists of air pump, diverter valve, check valve, and various air distribution lines necessary to inject fresh air adjacent to exhaust valves. Injection of fresh air adjacent to exhaust valves creates an afterburn which further consumes unburned gases in engine's exhaust.
CATALYTIC CONVERTER (CAT)
Converter is installed in vehicle's exhaust system to aid in reduction of exhaust emissions. This unit changes unburned hydrocarbons (HC) and carbon monoxide (CO) into water vapor and carbon dioxide.
COMPUTERIZED EMISSION CONTROL (CEC) SYSTEM
CEC system closely controls air/fuel ratio through a feedback system from an oxygen sensor in exhaust system. Major components of this system include exhaust gas oxygen sensor, vacuum switches, temperature switches, Micro Computer Unit (MCU) and special carburetor with stepper motor that controls air/fuel mixture. For additional information, see appropriate article in the COMPUTERIZED ENGINE CONTROL section.
EVAPORATIVE EMISSION CONTROL
All models use this closed tank (sealed) system, which returns raw fuel vapors and routes them to intake manifold for burning. Carbon canister stores vapors until engine draws them off for burning.
EXHAUST GAS RECIRCULATION (EGR)
EGR system uses vacuum operated EGR valve to introduce metered amounts of exhaust gas into engine's combustion chambers. This introduction of inert exhaust gas lowers peak combustion temperatures and thus lowers NOx formations.
POSITIVE CRANKCASE VENTILATION
Positive Crankcase Ventilation (PCV) system is used to control crankcase blow-by gases. This system takes blow-by gases from crankcase and recirculates them back into combustion chamber for reburning. Key device in PCV system is vacuum-controlled PCV valve.
PULSE AIR INJECTION
Pulse air injection system consists of check valves, control valves, control valve solenoids and various lines and hoses. Air is injected either at the front exhaust pipe or at catalytic converter, depending on engine operation. Injection of air into the exhaust system helps to complete the combustion of unburned gases.
SPARK CONTROL SYSTEMS
Jeep spark control systems are designed to control vacuum spark advance operation. Two systems are used: Coolant Temperature Override (CTO) and Non-Linear Vacuum Regulator (NLVR). CTO system improves driveability by alternating vacuum advance source between manifold vacuum and carburetor ported vacuum, depending upon temperature.
NLVR system supplies vacuum advance unit with regulated combination of manifold and carburetor ported vacuum when engine load is low and switches to supply only carburetor ported vacuum as load increases. In addition, forward delay valve, reverse delay valve, thermal vacuum spark control valve and vacuum spark control delay valve are used with various applications.
THERMOSTATIC AIR CLEANER (TAC)
TAC assembly is used to keep incoming air in carburetor at a stable temperature which is able to promote complete combustion (resulting in fewer emissions). System consists of a heat shroud at exhaust manifold, hot air hose, air cleaner assembly with thermal sensor, air door, vacuum motor and delay valve on all models.