Exhaust Gas Recirculation Systems
The EGR system was developed to reduce the formation of NOx emissions. NOx is created when the temperature of the combustion chamber climbs too high. The EGR valve allows inert exhaust gasses to flow into the combustion chamber (under specific conditions) which reduces the amount of air and fuel entering the combustion chamber. The result is cooler combustion temperatures improved fuel economy and a reduction in Oxides of Nitrogen.

EGR Valves may be operated via engine vacuum or electronically via the engine management computer. Vacuum controlled valves include single diaphragm, negative back-pressure, positive back-pressure designs. Computer controlled valves include pulse width modulated, integrated electronic, and digitally controlled.
Vacuum Controlled EGR
Digital EGR
Linear EGR
Electrically operated valves may use solenoids or motors to control the opening of the valve. Digitally operated valves use multiple solenoids that are connected to different size orifices. Depending on the operating condition one two or all three solenoids may be opened to allow the correct flow of exhaust gases into the intake system.
Vacuum operated EGR valves incorporate a spring controlled diaphragm connected to a pintle valve. When ported vacuum is applied to the diaphragm it overcomes the calibrated spring and the pintle valve opens a port allowing exhaust gasses to enter the intake system.

NOTE: When testing Positive Backpressure valve operation (GM applications) the valve must be installed and the engine must be running .

Linear EGR valves use a pulse-width modulated signal to activate the motor in order to control the opening of the EGR port. A sensor feedback signal indicates the amount of travel by the EGR pintle back to the PCM. This system allows for precise EGR flow into the intake system for each operating condition.