740 L4-2320cc 2.3L DOHC B234F (Can) (1992)
EVAP stands for Evaporative Emission and Is a system which deals with the gases evaporating from the fuel In the fuel tank. It prevents them being
emitted into the atmosphere.
Fuel vapor passes through a system of hoses from the fuel tank tiller opening through a roll-over valve into a carbon filter canister. This absorbs the
fuel vapor and prevents it from venting Into the atmosphere.
Carbon filter, canister
Fuel vapor from the tank is led into the top of the carbon filter and bonded to active carbon. Air is pushed out through a channel In the base of the
canister. Depending on the temperature etc. the carbon filter can adsorb about 90 g of fuel.
Roll-over valve
This closes when the car tilts sideways more than 45° and prevents fuel leaking out In the event of an accident.
Evaporative emission (EVAP) valve (vacuum)
This is located on the top of the carbon filter and is closed when the engine is not running. It is also closed when the engine is idling when it could
interfere with the automatic IAC system and the engine idle characteristics. The valve is controlled by a vacuum from the intake manifold which is
connected to the positive side of the throttle.
When engine load Increases the EVAP valve opens allowing fuel vapor to flow from the carbon filter to the intake manifold. Air is drawn in at the
same time through the channel in the base of the filter. Normally the carbon filter is emptied within 15-20 minutes.
Evaporative emission (EVAP) valve (electrical)
On the B234F the EVAP vacuum valve has been replaced with an electrical valve located between the canister and the Intake manifold. It works in
the same way as the vacuum valve.