S10/T10 Blazer 4WD V6-262 4.3L VIN Z (1994)
EGR Valve: Description and Operation
PURPOSE
The Exhaust Gas Recirculation (EGR) system is designed to lower NOx (oxides of nitrogen) emission levels created by high combustion temperatures.
EGR System
OPERATION
The EGR system routes exhaust gases from the exhaust manifold to the intake manifold at specified engine operating conditions. The EGR valve is
opened by ECM/PCM controlled vacuum and engine exhaust backpressure which allows exhaust gas to flow into the intake manifold. The exhaust gas
then moves with the air/fuel mixture into the combustion chamber. Since there is less air/fuel mixture to burn in the combustion chamber during EGR
operation, the temperature is reduced enough to limit NOx formation. 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. Variations in vacuum and exhaust backpressure, control the amount of exhaust gas recirculation.
EGR Valve
The port EGR valve is controlled by a flexible diaphragm which is spring loaded to hold the valve closed. Vacuum applied to the top side of the
diaphragm overcomes the spring pressure and opens the valve in the exhaust gas port. This allows the exhaust gas to be pulled into the intake manifold
and enter the engine cylinders.