Advanced EVAP System

Advanced EVAP System Identification

The system was introduced on all North American specification vehicles from October 1996 and the vehicles can be recognized by the information contained in the EVAP. FAMILY entry on the underbonnet Emission label (mounted on the vertical face of the bonnet lock platform).





A - Vehicles with advanced EVAPS
VLR1 1 24AYPFE

B - Vehicles without advanced EVAPS
VLR1 0 60AYPBC

System operation
The system is designed to prevent fuel vapor escaping to atmosphere, and consists of four roll-over valves fitted internally in the fuel tank, connected to the liquid/vapor separator by a nylon line. The separator is mounted to the side of the filler neck. An EVAP canister is positioned in the engine compartment mounted on the right front side valance, The liquid/vapor separator and EVAP canister are connected by a nylon line which runs the length of the chassis.

Pressure/vacuum relief valves are incorporated into the fuel filler cap and are designed to protect the fuel tank from permanent deformation in the event of system pressure or vacuum exceeding the system operating parameters. There are no other relief or one-way valves in the system.

A vent line flow restrictor known as an anti-trickle fill valve is fitted to the filler pipe in the line between the tank and EVAP canister. The function of this valve is to prevent overfilling the tank by trickling fuel in, thereby preserving the vapor space in the tank to allow for fuel expansion during hot weather.

The valve achieves this by blocking the vent line during the fuel filling process. The valve is operated by the action of inserting the filler gun so that when the fuel in the tank reaches the level of the filling breather, flow cut off occurs due to fuel filling the filler pipe.

During normal vehicle operation and when the engine is switched off, the venting system between the fuel tank and EVAP canister is open to allow the free passage of vapor.

The EVAP canister, which is connected by a nylon hose to the plenum chamber, absorbs and stores the fuel vapor from the fuel tank when the engine is not running. With the engine running, vapor is purged from the EVAP canister by allowing outside air to be drawn through the EVAP canister vent solenoid and link pipe by the influence of manifold vacuum to the EVAP canister purge connection on the canister.

Filter pads are fitted above and below the charcoal and in the EVAP canister vent solenoid to prevent the ingress of foreign matter into the purge line.

The EVAP canister purge valve, which is fitted in the line from the EVAP canister to the plenum, is controlled by the ECM which determines the most emission acceptable time at which purging should take place. This will normally be at engine speeds above idle and when the vehicle is in motion.

The EVAP canister vent solenoid is mounted on the side of the EVAP canister bracket and is connected to the EVAP canister by a length of large bore hose. The ECVS is controlled by the ECM and is normally open. The function of the ECVS is to block the air intake side of the EVAP canister. When the system receives an ECM signal the valve closes; this allows the system leak check to take place. The leak check only occurs when pre-determined vehicle operating conditions are met.