Sidekick 4WD L4-1590cc 1.6L SOHC 0 TBI 8V (1990)
Thermal Vacuum Valve: Description and Operation
The EGR system recirculates exhaust gas into the combustion chambers to reduce the formation of NOx. The operation of the EGR valve is controlled
by the EGR modulator which regulates the amount of vacuum applied to the EGR valve according to exhaust backpressure. Under low load conditions,
exhaust backpressure is low, allowing air to enter the vacuum passage, which reduces vacuum applied to the EGR valve resulting in less EGR flow.
Under higher load conditions, exhaust backpressure is high, causing full vacuum to be applied to the EGR valve resulting in maximum EGR flow. At
maximum load conditions (full throttle), manifold vacuum is low, resulting in minimal EGR flow. EGR operation is also controlled by coolant
temperature. When coolant temperature is low, the Bi-metal Vacuum Switching Valve (BVSV) on the intake manifold opens the EGR valve vacuum
passage to the atmosphere, causing the valve to remain closed. Once normal operating temperatures are reached, the BVSV closes and the EGR valve
operates according to the EGR modulator.
