General information
The system accumulates fuel vapors accumulated while the vehicle is parked and ensures that they are discharged into the intake manifold for combustion during normal engine operation.
Any EVAP system necessarily includes a special adsorber filled with activated carbon, which, in fact, collects fuel vapors. The method of removing vapors from the adsorber may vary depending on the design of a particular system. The following will allow the reader to understand in sufficient detail the principles of operation of any type of EVAP system.
Note. The described design does not necessarily have to fully correspond to the design of the system installed on a particular vehicle, however, the principle of operation is common to all models equipped with a fuel injection system. If any deviations are found, check the information on the VECI label.
The fuel filter cap is equipped with a two-way safety valve. In the event of a system failure, the valve ensures that fuel vapors are vented to the atmosphere.
Another two-way shut-off valve is installed on the fuel tank and provides adjustment of the fuel vapor removal to the carbon adsorber depending on pressure/vacuum changes associated with temperature changes.
After passing through the two-way valve, fuel vapors through the ventilation hoses enter the carbon adsorber, in which they accumulate during the entire parking time.
When the engine is started until it warms up to a certain temperature, the canister purge shut-off solenoid valve remains closed, allowing the purge diaphragm valve to open due to an increase in the depth of vacuum in the intake piping. From the adsorber, fuel vapors are blown out through the diaphragm valve into the intake manifold, from where they enter the combustion chambers, where they are burned out during the normal operation of the engine.
Examination
Note. A complete check of the EVAP system is beyond the skill level of the average amateur mechanic. Fortunately, the EVAP system, like other emission control systems, is backed by an additional 5 year/80,000 km warranty. Most often, failures of the EVAP system are associated with damage to the canister or failure of the vacuum hoses.
Vacuum hoses
1. Always check the condition of the vacuum hoses first, damage or disconnection of which is most often the cause of system failure (refer to the hose routing diagram on your vehicle's VECI label). Replace damaged hoses if necessary.
Purge control solenoid valve
1. The purge control solenoid valve removes accumulated fumes from the charcoal adsorber by creating a vacuum in the intake manifold. The valve provides vacuum when the engine is warm and remains closed when the engine is cold.
2. Make sure that the engine temperature does not exceed that indicated on the solenoid valve:
- 73°C for 1994 and 1995 models issue
- 68°С for models since 1996
3. Locate the purge hose at the top of the charcoal canister (see accompanying illustration). Refer to the hose routing diagram on the VECI label for warranty.
4. Having found the right hose, disconnect it from the adsorber and connect it to a vacuum gauge. Start the engine at idle - no vacuum should be created.
5. Wait for the engine to warm up - now the vacuum should appear.
6. At negative results of check find the electromagnetic valve of management of a purge on the inlet pipeline and disconnect from it electroconducting. Disconnect the vacuum hoses and connect a piece of rubber hose to one of the valve fittings.
7. Use the jumper wires to connect the valve directly to the battery. Try blowing the valve through the hose. When the battery is connected, the valve must be open and freely blown, when disconnected, it must be closed (some models use the opposite valve pattern).
8. At negative results of check replace the electromagnetic valve.
Two way valve
1. Remove the fuel filter cap.
2. Disconnect the fuel vapor line from the gas tank and connect the T-fitting to the vacuum pump and gauge (see accompanying illustration).
3. Slowly and continuously raising the depth of vacuum, follow the readings of the vacuum gauge. The vacuum should instantly stabilize at a value of 5.1 ÷ 15.2 mm Hg. Art. If the valve opens before the required vacuum is reached, replace it.
4. Switch the vacuum pump to the pressure port. Pressurize the line and read the vacuum gauge. The pressure should stabilize in the range of 10.2÷35.6 mm Hg. Art. (valve open).
5. If the valve opens before the desired vacuum is reached, replace it.
Canister vent shutoff valve
1. To determine if your vehicle is equipped with a canister vent check valve, look at the latter from above. If there is a 2-pin electrical connector on the cover, then a valve is provided.
2. Run hose from valve down to 3-way valve assembly from canister. Disconnect the hose from the three-way valve and connect it to the vacuum pump.
3. Remove the shut-off valve from the adsorber without disconnecting the electrical wiring and the vacuum pump from it.
4. Turn on the ignition (without starting the engine) and create a vacuum in the hose. If the valve holds a vacuum, disconnect the electrical connector. If the valve is still stuck, replace it.