DESCRIPTION
The Exhaust Gas Recirculation (EGR) system reintroduces exhaust gas into the combustion cycle resulting in lower combustion temperatures and reduced nitrous oxide (NOx) emissions.
The amount of exhaust gas and the timing of the cycle varies according to calibration as determined by engine speed, engine vacuum, exhaust system back pressure, coolant temperature and throttle opening. All EGR valves are vacuum actuated. See emission decal for vacuum diagram and calibration.
ELECTRONIC EGR VALVE SYSTEM
The Electronic EGR Valve System is controlled by the ECA. An EGR Valve Position sensor (EVP) mounted on top of the EGR valve sends an electrical signal to the ECA indicating the position of EGR pintle. (Scheme 27) Based on this information and engine requirements, the ECA sends an electrical signal to the Electronic Vacuum Regulator (EVR) to control vacuum to the EGR valve. On the 4.9L, the ECA signals the dual EGR Solenoid Vacuum Valves to control vacuum for EGR valve operation.
As vacuum is applied to the EGR valve, the diaphragm is actuated, lifting the pintle, allowing exhaust gas to flow through EGR valve into intake manifold. The amount of exhaust gas flowing through the EGR is proportional to the pintle position. This position is then signaled to the ECA.
Scheme 27
ELECTRONIC VACUUM REGULATOR
The Electronic Vacuum Regulator (EVR) is an electromagnetic device controlling vacuum output to the EGR valve. It's function is similar to the dual EGR Solenoid Vacuum Valve assembly which it replaces in most applications.
An ECA voltage is applied to the coil, inducing a magnetic field in the armature. The magnetic field acting on a metal disk closes an air vent. As the vent is closed, the vacuum signal to the EGR valve is increased and the EGR pintle lifts in accordance to the strength of vacuum signal.
EGR Control Solenoid (EGRC)
One of 2 solenoid vacuum valves, the EGRC solenoid controls the vacuum signal to the EGR valve. (Scheme 28) The EGRC is normally closed, no voltage is applied to the EGRC, and no vacuum signal flows through the solenoid. When voltage is applied to the EGRC, the valve pintle opens and the vacuum signal passes through the solenoid to the EGR.
EGR Vent Solenoid (EGRV)
The EGRV solenoid is used to vent the vacuum signal. The EGRV is normally open. If no voltage is applied to the EGRV, the vacuum vent remains open. This allows the vacuum signal to be vented to the atmosphere. When voltage is applied to the EGRV, the vent closes and the vacuum signal is trapped in the vacuum signal line.
Scheme 28
EGR VALVE POSITION (EVP) SENSOR
The EVP sensor input indicates the amount of EGR gases flowing into the intake manifold. When the EVP sensor indicates EGR gases are flowing, the Electronic Control Assembly (ECA) generally advances spark timing and the fuel injector pulse width is adjusted for changing EGR flow rates.
VACUUM RESERVOIR
The vacuum reservoir stores vacuum to allow EGR operation during periods of vacuum fluctuation or sudden drops in vacuum strength such as occur during acceleration.
ELECTRONIC EGR VALVE
Note. Electronic EGR valve system is controlled by the EEC system. This article covers testing of EGR valve only. See appropriate article in the COMPUTERIZED ENGINE CONTROL section for testing of EVP sensor and Electronic Vacuum Regulator.
- Check vacuum lines for correct routing. Disconnect vacuum hose at valve and connect vacuum gauge to hose. Disconnect connector at EVP on top of EGR valve.
- Start engine and apply 8 in. Hg (27.2 kPa) of vacuum with engine idling. Engine idle should become rough or stall. If idle did not drop, remove valve and check for plugged inlet or outlet ports. Clean ports if they are plugged. Replace valve if inlet or outlet ports are not plugged.