Emission Control Systems: Description and Operation

Fig 40 Fuel Tank Mounting:

EVAPORATION (EVAP) CONTROL SYSTEM
The function of the EVAP control system is to prevent the emissions of gasoline vapors from the fuel tank into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to a carbon filled EVAP canister. They are temporarily held in the canister until they can be drawn into the intake manifold when the engine is running.

All engines use a duty cycle purge system. The JTEC controls vapor flow by operating the duty cycle EVAP purge solenoid. Refer to Canister Purge (Duty Cycle) Solenoid for additional information.

The EVAP canister is a feature on all models for the storage of fuel vapors from the fuel tank.

NOTE: The hoses used in this system are specially manufactured. If replacement becomes necessary, it is important to use only fuel resistant hose.

ROLLOVER VALVES
The fuel tank is equipped with 2 interconnected rollover valves. The valves are located on the top of the fuel tank. These valves will prevent fuel flow through the fuel tank vent (EVAP) hoses in the event of an accidental vehicle rollover. The EVAP canister draws fuel vapors from the fuel tank through these valves.

The valves may be serviced separately.

Fig 2 EVAP Canister Location:

EVAP CANISTER
A sealed, maintenance free, EVAP canister is used on all vehicles. The canister is mounted under the right side of vehicle behind the wheel well (Fig. 2).

The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister. Fuel vapors are temporarily held in the canister until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canister to be purged at predetermined times and at certain engine operating conditions.

Fig 9 Crankcase Breather Filter:

CRANKCASE BREATHER/FILTER
The crankcase breather/filter (Fig. 9) is located on the cylinder head (valve) cover. The filter may be cleaned by washing it thoroughly in kerosene or an equivalent. Filter must be thoroughly drained. More frequent service may be necessary for vehicles operated extensively on short run, stop and go, extended engine idle service or extreme dust conditions.