DeVille V8-4.9L VIN B (1995)
EGR Valve: Description and Operation
Exhaust Gas Recirculation
Positive Backpressure EGR Valve
EGR VALVE
This vehicle uses a positive backpressure Exhaust Gas Recirculation (EGR) valve. A positive backpressure EGR valve requires exhaust
backpressure (proportional to engine flow) to open and allow exhaust gas to flow into the intake manifold. For this reason, careful diagnosis of the
system is important so that outside conditions (such as an exhaust backpressure) will not lead to misdiagnosis. A failed on EGR solenoid will not
pass EGR gases at idle unless there is a restriction in the exhaust system increasing backpressure.
The Powertrain Control Module (PCM) uses the following sensors to control the EGR solenoid:
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Engine Coolant Temperature (ECT) Sensor.
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Throttle Position (TP) Sensor.
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Manifold Absolute Pressure (MAP) Sensor.
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Intake Air Temperature (IAT) Sensor.
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Throttle Position (ISC) Switch.
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RPM data from distributor reference pulses.
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Vehicle Speed Sensor (VSS).
Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stop. With too much EGR flow at idle, cruise, or cold
operation, any of the following conditions may occur:
