DESCRIPTION
The exhaust gas recirculation (EGR) system is used to help control formation of NOx emissions. By recycling a limited amount of exhaust gas back to the intake system, combustion temperatures are lowered, which helps keep NOx emissions down.
The system consists of EGR valve, EGR pipe, thermostatic valve, control valve orifice and vacuum outlet.
The EGR system operates differently for non-turbo and turbo, but the thermostatic valve, which deactivates the EGR system below 112°F (43°C), is controlled by coolant temperature in both systems.
Exhaust gases (from exhaust port of number 2 cylinder) are routed through the cylinder head, and then through a steel pipe, to EGR valve in inlet manifold. (Схема №1)
Opening of the EGR valve, when coolant temperature is below 112°F (43°C), is regulated by 2 adjacent vacuum ports in throttle valve housing. At idle, vacuum is not applied to either port, resulting in a closed system. (Схема №2)
At off-idle or low speed cruise, vacuum is applied to port number 1 only, resulting in a partial signal to (and a partial opening of) the EGR valve. When throttle valve opens past the second port, a full vacuum signal is applied to the EGR valve.
Exhaust gases (from exhaust port of number 2 cylinder) are routed through the cylinder head, and then through a steel pipe, to EGR valve in inlet manifold. (Схема №3)
Opening of the EGR valve, when coolant temperature is below 112°F (43°C), is regulated by a vacuum port in throttle valve housing. At idle, vacuum is not applied to the port, resulting in a closed system.
When engine speed reaches 1900 RPM, vacuum is applied to the port resulting in a full signal to (and a full opening of) the EGR valve. A special size orifice, depending of type of transmission used, allows only a certain amount of exhaust gas to reach EGR valve.
- Run engine at normal operating temperature. Connect a tachometer to engine. Slowly raise engine speed, at note RPM at which valve begins to open. The valve spindle is visible between valve casting and valve bellows.
- On Turbo models, the valve should open at 2300-2900 RPM. On all other models, valve should begin to open at 1900 RPM. If necessary, check EGR valve and thermostatic valve.
EGR VALVE
With engine idling, disconnect EGR valve vacuum hose at thermostatic valve. Connect a vacuum pump to hose. Operate vacuum pump to create a vacuum within EGR valve. The engine idle quality should diminish, and the engine should die. If idle quality does not diminish, clean or replace EGR valve.
THERMOSTATIC VALVE
Disconnect the thermostatic valve vacuum hoses at EGR and vacuum port on throttle valve body. Blow through valve. When engine is cold, valve should be closed. Run engine at normal operating temperature. When engine is warm, valve should be closed. Replace thermostatic valve if inoperative.