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. The EGR cooler assists in reducing exhaust gas temperature before it is cycled into combustion chamber. This helps further reduce high temperatures that cause NOx formation.
VACUUM MODULATOR
- Disconnect vacuum hoses from ports "P", "Q" and "R" of vacuum modulator. Plug ports "P" and "R" (2 ports on same side) and blow through port "P" (single port on opposite side). Air should escape freely from filter.
- Start engine and run at 2000 RPM on Camry, 3000 RPM on Celica, Pickup and 4-Runner, or 2500 RPM on all other models. Repeat blowing test. There should be strong resistance to air flow through modulator. If not, replace modulator. Reconnect vacuum hoses to proper locations.
BI-METALLIC VACUUM SWITCHING VALVE (BVSV)
- Drain coolant and remove BVSV valve. Place sensing portion in cool water, but do not allow water into valve.
- Cool BVSV to below 86°F (30°C). Blow air into top port and check that air does not escape through bottom port.
- Heat BVSV to above 111°F (44°C). Blow air into top port and check that air escapes through bottom port.
- Apply liquid sealer to threads of BVSV and reinstall. Fill radiator with coolant. If problem is found, replace BVSV.
Scheme 17
- Connect battery voltage to VSV terminals. (Scheme 17) Blow air into port "E" (nearest valve) and check that air comes out port "F" (farthest from valve). Disconnect battery and repeat test. Air should come out front port ("G"). (Scheme 17): Vacuum Switching Valve (VSV) Test Connections
- Using an ohmmeter, check that there is no continuity between positive terminal and body of VSV. Resistance between terminals should measure 38-43 ohms at 68°F (20°C). Replace valve if it does not meet specifications.
Scheme 18
- Check and clean vacuum modulator filters with compressed air before proceeding with test. Using a 3-way connector, connect a vacuum gauge to the hose between EGR valve and EGR vacuum modulator.
- Check seating of EGR valve by starting engine. Engine should start and run at idle.
- Check BVSV with coolant temperature below 86°F (30°C). Vacuum gauge should indicate low vacuum at 2500 RPM. (Scheme 18): EGR System
- Warm engine to normal operating temperature. Vacuum gauge should indicate low vacuum at 2500 RPM.
- Disconnect vacuum hose from port "R" of EGR vacuum modulator and connect port directly to intake manifold vacuum. Vacuum gauge should indicate high vacuum at 2500 RPM. Disconnect vacuum gauge and reconnect hoses to proper locations. NOTE: This will cause slight engine misfire due to a large amount of exhaust gas being injected into intake manifold.
- 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.
- Check computer control of vacuum switching valve (VSV). Disconnect vacuum hoses from ports "E" and "F" of VSV. (Scheme 19) With engine idling, blow into port "F". The valve should close and not allow air to escape through port "E".
- Increase engine speed to above 1500 RPM. Again blow into port and note that valve should open to allow air to escape from port "E". If no problem is found with this inspection, system is okay.
