Exhaust Gas Recirculation: Description and Operation

Digital EGR Valve:

The digital EGR valve is designed to accurately supply EGR to the engine without the use of manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through three size incremented orifices, to produce seven combinations. When the solenoid is energized, the armature , with attached shaft and swivel pintle, is lifted opening the orifice.
The flow accuracy is dependent on the metering orifice size only, which results in improved control. The swivel pintle feature insures good sealing of the exhaust gas, reducing the need for critical assembly alignment. The effects of EGR leakage on idle quality are reduced because the shaft and seals are exposed to the exhaust pressure instead of manifold vacuum. The shafts are sealed from the exhaust chamber by floating seals held in place by the seal spring. These springs also hold the upper seals that seal the armature cavity in the solenoids.
The solenoid coils are fastened together to maximize reliability and to seal the coils from the environment. The coils use a common power terminal with individual ground terminals.
The digital EGR valve is opened by the ECM Quad Driver, grounding each respective solenoid circuit. This activates the solenoid, raises the pintle, and allows exhaust gas to flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters combustion will not occur. Because of this, very little exhaust gas is allowed to pass through the valve, especially at idle. the valve should only open when the engine is at operating temperature and above idle speed.

EGR CONTROL
To regulate EGR flow, the ECM controls the EGR solenoids to vary the amount of EGR flow. The ECM uses the information from the the following sensors to control the flow:
Coolant temperature
Throttle Position (TPS)
Mass Air Flow (MAF)