The emission control devices required on a Blazer or Jimmy are determined by the weight classification. Light duty models use the same emission controls as passenger cars; these are all 1969-74 models, 1975 two wheel drive models and all 1979-82 models. Heavy duty models operate under less stringent rules and use a few less emission control devices; these are 1975 four wheel drive models and all 1976-78 models.
Positive Crankcase Ventilation (PCV) was the earliest form of automotive emission control, dating back to 1955 on General Motors vehicles. Still in use today, it routes cylinder fumes from the crankcase through a PCV valve and back into the combustion chamber for reburning.
In 1966, the Air Injector Reactor (AIR) system was introduced on General Motors vehicles to satisfy California emission requirements. This system pumps oxygen to the exhaust gases as they exit from the cylinder, where they are ignited and burned more completely to further reduce hydrocarbon and carbon monoxide exhaust emissions.
General Motors introduced the Controlled Combustion System (CCS) in 1968, which uses various components and design calibrations to further reduce pollutants.
Combined Emission Control (CEC) and Transmission Controlled Spark (TCS) have been used since 1970 and basically do not allow distributor vacuum advance in Low gear.
In 1973, the Exhaust Gas Recirculation (EGR) system was developed in response to more stringent Federal exhaust emission standards regarding oxides of nitrogen (NO x ). Oxides of nitrogen are formed at higher combustion chamber temperatures and increase with higher temperatures. The EGR system is designed to reduce combustion temperature thereby reducing the formation of NO x .
The Evaporative Control System (ECS) and the Early Fuel Evaporation System (EFE) are designed to control fuel vapors that escape from the fuel tank and carburetor through evaporation. These systems seal the fuel tank to retain vapors in a charcoal canister. The canister is purged and the vapors burned during engine operation.
The Pulse Air Injection Reactor (PAIR) system was introduced in 1979 on the six cylinder. Through the use of exhaust gas back-pressure, air is injected into the exhaust system to further the exhaust gas burning process.
Certain late model engines are equipped with Electronic Spark Control (ESC). The ESC controls engine detonation by adjusting spark timing.
The following sections are devoted to the description and service of each separate system.