Fuel Evaporative Emissions Reduction System — Design and Testing (Hyundai Elantra J1)

The main element of this system is a carbon filter located in the engine compartment.

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At idle, when the engine is not yet warmed up, fuel vapors added to the balanced mixture cause excess emissions of toxic substances through the exhaust pipe. Because of this, one of the throttle body orifices of the fuel injection system is used to direct fuel vapors to the filter only after the throttle valve is opened wider than the idle position. If there is no vacuum, the filter purge valve will not open.

When the filter purge valve opens, air is sucked in under a slight vacuum from the air intake. If operational problems arise during engine warm-up, and all settings and adjustments of the main fuel system and engine are correct, the operation of the thermal valve should be checked.

Checking system elements

Purge control valve

Check the condition of all hoses and connections. Many problems often arise due to unreliable connections in the system or limited hose capacity.

Check the valve (1) by removing the valve from the vehicle and connecting a hand vacuum pump to the valve vacuum port. The valve must maintain a vacuum.



Reduce the vacuum and apply a low pressure air flow into the hose connection located on the side surface of the filter.

If there is no vacuum, air should not pass through the valve. Reduce the vacuum to 150 mm Hg. Re-introduce air into the pipe. Air must pass through the valve.

The carbon filter is regulated by a solenoid purge control valve. With the engine off, disconnect the two vacuum hoses leading to the valve.

Disconnect the electrical supply wire from the valve. Connect the hand vacuum pump to the port where the hose was connected. Create some vacuum using the pump; it must be preserved.

Connect the battery to the solenoid valve terminals.



The polarity must be observed absolutely precisely. Connect the positive terminal to the terminal that forms the "top" of the "T". After applying voltage to the solenoid valve, the vacuum should decrease as the hand pump operates.



Disconnect the battery and check the resistance at the solenoid valve terminals. The resistance value should be 36-44 Ohms at 20°C.

Note: Remember that the resistance value changes depending on temperature.

Thermovalve

Thermal valves are installed on the intake manifold or cylinder head so that their bottom is immersed in the coolant. (On later model engines, the purge system is controlled by the fuel injection computer). The thermal valve provides a delay or passage of vacuum to the purge control valve depending on the coolant temperature. Perform the check on a cooled engine.

Disconnect the two vacuum hoses on the thermostat valve. With the engine off, connect a hand vacuum pump to the top port on dual port valves or to the single port.



Apply vacuum and verify that the valve is leaking or does not retain vacuum.

Start and warm up the engine. After the coolant has warmed up to operating temperature, disconnect the corresponding hose and repeat the check. The valve must maintain a vacuum.

Replace the thermal valve only on a cold engine.

Overflow limiter (two-way valve)

This device, sometimes mistaken for a fuel filter, is installed on the steam line leading from the tank to the carbon filter. Typically located on or near the tank, this valve is sensitive to both compression and vacuum. It is designed to compensate for pressure drops that occur in the tank.



When excess pressure is created in the tank, for example due to high air temperatures or after driving a significant distance, the valve releases the pressure and vapors into the carbon canister, thereby venting the tank and preventing the vapor level from increasing. And, conversely, when a vacuum is created in the tank, the valve will release some air from the filter into the tank.

Warning: If you hear a sound coming from the rear of your vehicle (even with the engine off), then this is the sound of this valve operating when it releases pressure. To eliminate this sound, you need to unscrew the fuel filler cap and screw it back on.

Replacing the valve can only change the tone of the sound, but the sound itself is preserved in most cases.

To check, do the following:

• Remove the valve from the steam line.
• Blow lightly through the valve on each side. If air passes with some resistance, the valve is working.
• Connect the valve to the line in the appropriate direction and secure the clamps. Before installing the clamps, make sure that the lines are securely installed on the pipes.

Gravity valve

This valve is located in the steam line leading from the tank to the carbon filter. The valve prevents gasoline from leaking from the fuel tank into the system if the vehicle rolls over in a traffic accident. Under normal conditions, vapors are supplied through this line, which are easily absorbed and retained by the filter's carbon mass.

When the car turns over, the line fills with liquid gasoline. Therefore, the gravity valve closes the fuel line and keeps the fuel in the tank.



To check, you need to remove the valve and disconnect the hoses from it. If you hear a clicking sound when you shake it, it is working properly.

Carbon filter

The carbon filter should be checked periodically for cracks, blockages and secure hose connections. On many models, the carbon filter is replaced after a certain period of time or a certain number of kilometers.