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Fuel Evaporation System Volkswagen Golf Mk1

Testing & Diagnostics 3 illustrations ~387 words

DESCRIPTION

The sealed fuel evaporation system prevents fuel vapors from escaping into the atmosphere. The system consists of a fuel tank, expansion tank(s), activated charcoal canister, fuel tank breather gravity valve(s), control valve, and connecting lines and hoses.

Fig. 1: Fuel Evaporation System (Jetta & Golf)
Scheme 1: Fuel Evaporation System (Jetta & Golf)

OPERATION

As fuel expands in tank, fuel laden vapors are forced out of tank through an upper vent port. On all models except Vanagon, vapors flow up through a gravity valve and into an expansion tank where liquid fuel condenses and returns to fuel tank as temperature drops.

Canister to Intake Manifold Flow (Cabriolet, Scirocco & Quantum). Scheme 3

Scheme 3: Canister to Intake Manifold Flow (Cabriolet, Scirocco & Quantum)
Scheme 3: Canister to Intake Manifold Flow (Cabriolet, Scirocco & Quantum)

Fuel vapors then flow from an upper vent port on expansion tank, through a control valve, and into the charcoal canister where they are absorbed until manifold vacuum pulls them out of canister for burning.

When the engine is running above idle, a vacuum signal opens control valve and canister vapors are drawn from canister through control valve and into intake manifold for burning.

EVAPORATIVE EMISSION CONTROL VALVE

  1. Remove hose leading to canister from control valve and blow air into valve. Check that air flow is blocked and that air does not leak from valve seams.
  2. Remove hose from control valve's vacuum advance port. Remove vacuum retard hose from distributor and connect it to control valve's vacuum advance port. Remove hoses from 2 other valve ports.
  3. Start engine and blow air into valve's canister port. Check that air flow is blocked and that air does not leak from valve seams. Replace valve if it does not operate as outlined.

GRAVITY VALVE

  1. Remove hoses from gravity valve and remove valve from body above and to the right of the fuel tank. (Scheme 4) Attach one end of a hose to valve's expansion tank port and submerge the other end of hose in a container of water.
  2. Hold valve vertically and blow into valve's port to fuel separator. Check that air flows through valve into water. Gradually tilt valve while blowing air into it and check that air stops flowing through valve when it is tilted at a 45° angle. Replace valve if it does not operate as outlined.

Checking Gravity Valve Operation Hold valve vertically when testing. Scheme 4

Scheme 4: Checking Gravity Valve Operation Hold valve vertically when testing.
Scheme 4: Checking Gravity Valve Operation Hold valve vertically when testing.

MAINTENANCE

Every 15,000 miles visually inspect the entire system. Check for leaks and damaged or deteriorated hoses and components.

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