EGR System - Gasoline Toyota Tercel L20

DESCRIPTION

The exhaust gas recirculation (EGR) system is used to reduce the formation of NOx emissions by reducing combustion temperature. This is accomplished by recycling metered amounts of exhaust gas back into the intake system.

Each system has a vacuum-operated EGR valve and a vacuum modulator. All models use temperature sensing devices for controlling EGR operation.

The device used could be a vacuum switching valve (VSV), a bi-metallic vacuum switching valve (BVSV), a thermostatic vacuum switching valve (TVSV), or a combination of these valves. A check valve, EGR cooler and computer can also be used on some models.

OPERATION

When engine is not at operating temperature, no exhaust gas recirculation will occur since the switching valve is closed. Once engine temperature increases, the switching valve opens and exhaust gas recirculation is then controlled by other components of the system.

Vacuum modulator reacts to relieve exhaust backpressure, and to balance atmospheric pressure and vacuum to allow or stop EGR.

VACUUM MODULATOR

1. Disconnect vacuum hoses from both ports of vacuum modulator. Plug port nearest EGR valve and blow air into port farthest from EGR valve. Air should escape freely through air filter of modulator.
2. Start engine and maintain engine speed at 3000 RPM. Repeat blow test. There should be strong resistance to air flow. If not, replace vacuum modulator. Reconnect vacuum hoses to proper locations.

THERMOSTATIC VACUUM SWITCHING VALVE (TVSV)

1. Drain coolant from radiator and remove TVSV. Place threaded end of valve in container of ice water with thermometer. With temperature below 45°F (7°C), check that air flows from port "J" to ports "L" and "M" and from port "K" to port "N". (Scheme 19)
2. Heat water to 63-122°F (17-50°C). Check that air flows from port "K" to ports "N" and "L" and from port "J" to port "M".
3. Continue heating water to above 154°F (68°C). Check that air flows from port "K" to ports "M" and "L" and does not flow from port "J" to any other port.
4. Apply liquid sealer to threads of TVSV and reinstall. Fill radiator with coolant. If problem is found, replace TVSV.

Testing Thermostatic Vacuum Switching Valve (TVSV). Scheme 19

CHECK VALVE

Disconnect vacuum hoses and remove valve. Blow through valve. Air should flow from Orange side to Black side, but not from Black to Orange. Replace valve if it does not perform as outlined.

Scheme 20

1. Check and clean vacuum modulator filters with compressed air before proceeding with test. Disconnect vacuum hose from EGR valve and, using a "T" connector, connect a vacuum gauge. Check that engine starts and runs at idle.
2. Check TVSV with coolant temperature below 122°F (50°C). Check that vacuum gauge indicates zero at 3000 RPM. (Scheme 20): EGR System
3. Check TVSV and EGR vacuum modulator with engine hot. Vacuum gauge should indicate low vacuum at 3000 RPM.
4. With engine idling, apply vacuum directly to EGR valve. Engine should run rough or die. Remove vacuum and reconnect vacuum hoses to proper locations. Engine should run smooth. If no problem is found with this inspection, system is okay.