GM Full-Size Trucks 1970-1979 Repair Guide

VACUUM DIAGRAMS

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Following are vacuum diagrams for most of the engine and emissions package combinations from 1977-79. The diagrams dipicted here are also representitive of the types of emission controls that can be found on engines used in the 1970-76 models. Because vacuum circuits may vary based on year, various engine and vehicle options, always refer first to the vehicle emission control information label, if present. Should the label be missing, or should vehicle be equipped with a different engine from the vehicle's original equipment, refer to the diagrams below for the same or similar configuration.

If you wish to obtain a replacement emissions label, most manufacturers make the labels available for purchase. The labels can usually be ordered from a local dealer.

See Figures 1 through 30





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Fig. Fig. 1: Vacuum hose schematic - 1977 250 engine, light duty emissions

 


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Fig. Fig. 2: Vacuum hose schematic - 1977 250 and 292 engines, heavy duty emissions (except California)

 


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Fig. Fig. 3: Vacuum hose schematic - 1977 292 engine, heavy duty (California)

 


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Fig. Fig. 4: Vacuum hose schematic - 1977 305 engine, light duty low altitude emissions

 


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Fig. Fig. 5: Vacuum hose schematic - 1977 305 engine, heavy duty emissions

 


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Fig. Fig. 6: Vacuum hose schematic - 1977 350 engine, light duty high altitude and California emissions

 


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Fig. Fig. 7: Vacuum hose schematic - 1977 350 engine, light duty low altitude emissions

 


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Fig. Fig. 8: Vacuum hose schematic - 1977 350 and 400 engines, heavy duty emissions (except California)

 


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Fig. Fig. 9: Vacuum hose schematic - 1977 350 and 400 engines, heavy duty emissions (California)

 


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Fig. Fig. 10: Vacuum hose schematic - 1977 400 engine, heavy duty California emissions with A/C

 


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Fig. Fig. 11: Vacuum hose schematic - 1977 454 engine, light duty emissions

 


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Fig. Fig. 12: Vacuum hose schematic - 1977 454 engine, heavy duty emissions (except California)

 


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Fig. Fig. 13: Vacuum hose schematic - 1977 454 engine, heavy duty emissions (California)

 


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Fig. Fig. 14: Vacuum hose schematic - 1978 250 engine, light duty emissions (except California)

 


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Fig. Fig. 15: Vacuum hose schematic - 1978 250 engine, light duty emissions (California)

 


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Fig. Fig. 16: Vacuum hose schematic - 1978 250 and 292 engines, heavy duty emissions (except California)

 


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Fig. Fig. 17: vacuum hose schematic - 1978 292 engine, heavy duty emissions (California)

 


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Fig. Fig. 18: Vacuum hose schematic - 1978 305 engine, light duty low altitude emissions

 


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Fig. Fig. 19: Vacuum hose schematic - 1978 305 engine, heavy duty emissions

 


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Fig. Fig. 20: Vacuum hose schematic - 1978 350 engine, light duty low altitude emissions

 


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Fig. Fig. 21: Vacuum hose schematic - 1978 350 engine, light duty emissions (California)

 


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Fig. Fig. 22: acuum hose schematic - 1978 350 and 400 engines, light duty emissions with A/C

 


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Fig. Fig. 23: Vacuum hose schematic - 1978 350 and 400 engines, heavy duty emissions with A/C

 


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Fig. Fig. 24: Vacuum hose schematic - 1978 350 and 400 engines, heavy and light duty emissions with A/C (California)

 


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Fig. Fig. 25: Vacuum hose schematic - 1978 454 engines, light duty emissions

 


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Fig. Fig. 26: Vacuum hose schematic - 1978 454 engines, heavy duty emissions (except California)

 


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Fig. Fig. 27: Vacuum hose schematic - 1978 454 engines, heavy duty emissions (California)

 


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Fig. Fig. 28: Two canister system vacuum hose schematic - 1978 models

 


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Fig. Fig. 29: Vacuum hose schematic - 1978 350 diesel engines, light duty emissions

 


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Fig. Fig. 30: Vacuum hose schematics - 1979 models

 

 
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