Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Evaporative Emission Controls

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OPERATION



See Figures 1 and 2

This system prevents the escape of raw fuel vapors. It consists of a sealed carburetor (when applicable), an unvented fuel tank cap, a tank expansion chamber, a filter canister and connector hoses. Vapors which reach the filter deposit hydrocarbons on the charcoal element. Fresh air enters the filter with the engine running and forces hydrocarbons to the air cleaner where they join the air/fuel mixture and are burned. Many 1979 and later models use a charcoal filter valve which prevents vapors from escaping when the engine is OFF .



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Fig. Fig. 1: Schematic of an evaporative emission control system on carbureted engines



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Fig. Fig. 2: Evaporative emission control system components on Digifant engines

SERVICE



Maintenance of the system consists of checking the condition of the various connector hoses and the charcoal filter. All worn or damaged components should be replaced.

REMOVAL & INSTALLATION



Removal and installation of the evaporative emission control system components consists of labeling and disconnecting hoses, loosening retaining screws and removing the part which is to be replaced from its mounting point.

When replacing any EVAP system hoses, always use hoses that are fuel-resistant or are marked EVAP. Use of hoses which are not fuel-resistant will lead to premature hose failure.

 
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