GM Full Size Vans 1967-1986 Repair Guide

General Information


The emission control devices required on these vans are determined by the weight classification. Light duty models use the same emission controls as passenger cars:

All 1967-69 models
1970-71 G-10, 1500, 20, 2500 models
1972-73 G-10, 1500, 20, 2500 models
1972-73 G-30, 3500 passenger models
1974-78 G-10, 1500 models
All 1979 and later models

Heavy duty models operate under less stringent rules and use less emission control devices. These include:

1971 G-30, 3500 models
1972-73 G-30, 3500 models (except passenger vans)
1974-78 G-20, 2500, 30, 3500 models

Positive Crankcase Ventilation (PCV) was the earliest form of automotive emission control, dating back to 1955 on Chevrolet vehicles. Still in use today, it routes cylinder blow-by gases from the crankcase through a PCV valve and back into the combustion chamber for reburning.

In 1966, the Air Injection Reactor (AIR) system was introduced to satisfy the 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 emission.

Chevrolet introduced the Controlled Combustion System (CCS) in 1968, which uses various components and design calibrations to further reduce pollutants.

The 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 (Nox). 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 NOx.

The Evaporative Control System (ECS) is designed to control fuel vapors that escape from the fuel tank and carburetor through evaporation. This system seals the fuel tank to retain vapors in a charcoal canister. The stored vapors are burned during engine operation.