Exhaust Gas Recirculation: Description and Operation
Fig. 47 EXHAUST GAS RECIRCULATION SYSTEM (DIESEL):
The E.G.R. system (applicable to California market only) reduces the amount of nitrogen oxides (NOx) in the exhaust by recirculating exhaust back into the intake manifold. The E.G.R. system operates in proportion to the opening of the throttle lever. The controlling vacuum is taken from the engine vacuum pump. The exhaust gas recirculation is gradually decreased with engine load and is completely shut off at high engine load. The smoke and hydrocarbons in the exhaust would be high if the E.G.R. system operated at high engine loads. Also, the fuel consumption and engine life would be impaired. Fig. 47.
Fig. 54 EXHAUST GAS RECIRCULATION SYSTEM (TURBO DIESEL):
E.G.R. component placement on D24T (turbo) engine. Fig. 54.
COMPONENTS:
----------------
Fig. 48 THERMO-VACUUM VALVE:
THERMO-VACUUM VALVE
Opens the controlling vacuum line when the engine water temperature has reached about 45°C (113°F). The E.G.R. system does not operate on a cold engine. When cold, the engine produces only small amounts of nitrogen oxides and the amount of hydrocarbons and exhaust gas smoke would be increased if the E.G.R. system operated. Fig. 48.
Fig. 49 IDLE SWITCH:
IDLE SWITCH
Controlled by a cam on the injection pump lever. Above idle speed, the idle switch signals the E.G.R. relay to cut out the control voltage to the solenoid valve for about 5 seconds. This decreases the smoke and hydrocarbon emissions when accelerating from idle. Fig. 49.
Fig. 50 VACUUM GOVERNOR:
VACUUM GOVERNOR
Controlled by a cam on the injection pump lever. The vacuum governor controls the vacuum going to the E.G.R. valve. When the throttle opening on the engine is increased, the control vacuum to the E.G.R. valve is decreased. The decrease in vacuum to the E.G.R. valve causes a decrease in the amount of exhaust gases being recirculated. A switch incorporated in the vacuum governor controls the E.G.R. solenoid valve. This switch cuts off vacuum to the E.G.R. valve at high engine vacuum. The solenoid valve voltage disappears and the E.G.R. system is disengaged. Fig. 50.
Fig. 51 OVERDRIVE RELAY:
OVERDRIVE RELAY
Cuts out the voltage to the solenoid valve when the overdrive is engaged. The E.G.R. system then is inoperative. When driving in overdrive, the engine load is moderate and relatively constant. As a result, the emission of nitrogen oxides is low and no E.G.R. is needed. Fig. 51.
Fig. 52 SOLENOID VALVE:
SOLENOID VALVE
The solenoid valve controls the vacuum to the E.G.R. valve. Fig. 52.
Fig. 53 E.G.R. VALVE:
E.G.R. VALVE
The E.G.R. valve controls the recirculation of exhaust gases to the intake manifold. The valve is controlled by a vacuum line. Vacuum applied to the E.G.R. valve causes it to open and allows exhaust gases to recirculate into the intake manifold. Fig. 53.