Checking The Mercedes Benz Fuel Evaporation Systems

The Mercedes Benz fuel evaporation system is designed to prevent fuel vapor from escaping from the fuel tank and entering the atmosphere. The Mercedes Benz systems include a fuel tank with vapor separator, purge valve, Thermo valve, and charcoal canister and vent valve.

OPERATION EVAPORATION SYSTEM

ENGINE NOT RUNNING

Fuel tank pressure is maintained by the vent valve, which is a pressure relief valve. When engine is off and vapor expands heated by sun, the pressure relief valve in vent valve opens, allowing vapor to escape threw charcoal canister.

PURGE SYSTEM ENGINE RUNNING

The purge valve is installed in vacuum line between throttle valve housing and the charcoal canister

A vacuum control line is routed from throttle valve housing through a thermo valve and to the purge valve. When the engine is running, throttle valve position is above idle, and engine coolant is above 122°F, the canister purging takes place. As the throttle is opened further, more vacuum is applied to the canister and purge rate continues.

Fuel Evaporation System testing

Disconnect the hose between purge valve and the canister at canister. Place a finger over hose end. Slowly increase engine speed to 3000 R.P.M. No vacuum should be present. 1At idle; vacuum should gradually increase with engine speed.

2. If no vacuum was present at hose, trace hose back to throttle valve housing. Blow through connection on housing and ensure the hose is clear. 3. If vacuum is still not present, then remove White Purple and Black hose from purge valve. If vacuum is now present, replace purge valve. If vacuum is not present, replace thermo valve.

MAINTENANCE

Check fuel lines tank, and hoses for leaks or damage, and deterioration at first 1000 mile service and every 15,000 miles thereafter.

Clint Hough is an author and web site publisher on imported car parts and you can get all your Mercedes Benz Parts from our on line catalog for all your Mercedes Car Parts needs at Imported car parts.com.
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