Fleetwood FWD V8-273 4.5L (1988)
EGR Vacuum Solenoid Valve: Description and Operation
The ECM controls the vacuum to the EGR valve with a solenoid valve. A constant ignition voltage is applied to the positive terminal of the EGR
solenoid. The vacuum supply to the EGR valve is regulated by the ECM which controls the ground to the EGR solenoid.
The percentage of time that the ECM grounds the EGR solenoid is called the solenoid duty cycle. The duty cycle is the time the solenoid is ON divided
by the time it is OFF. A duty cycle of 0% will enable the EGR valve (turn EGR full on) since a de-energized solenoid allows vacuum to pass to the EGR
valve. A duty cycle of 100% will turn the EGR valve full off since the solenoid will be energized and will not allow vacuum to flow to the EGR valve.
The EGR duty cycle is regulated by the ECM depending on engine load conditions. When the engine is cold, within a specified load range, and above a
specified engine speed, the solenoid valve sends 100% duty cycle to the solenoid and blocks vacuum to the EGR valve. When the engine is warm, the
ECM sends a signal to the solenoid to allow the EGR to operate.
The ECM uses the following sensor inputs to control the EGR solenoid:
1. Coolant Temperature Sensor (CTS)
2. Throttle Position Sensor (TPS)
3. Manifold Absolute Pressure (MAP)
4. Idle Speed Control (ISC)
5. Engine speed data from distributor reference pulses.
