DESCRIPTION & OPERATION
Note. The following information applies to V6 and V8 diesel engines only. The 1.8L diesel does not use an EGR system.
To lower the formation of oxides of nitrogen (NOx), it is necessary to reduce combustion chamber temperatures. This is accomplished by introducing exhaust gases into the combustion chambers.
V6 ENGINES
On V6 diesel engines, vacuum from the vacuum pump is modulated by the vacuum regulator valve (VRV) mounted on the injection pump. Vacuum is highest at idle and decreases to zero at wide open throttle. The EGR valve is designed to open to its maximum at idle and close at wide open throttle.
The amount of EGR valve opening is further modulated by a vacuum modulator valve (VMV). The VMV allows for an increase in vacuum to the EGR valve as throttle is closed, up to the switching point of the VMV.
A response vacuum reducer (RVR) valve is used between the VRV and the torque converter clutch (TCC) operated solenoid. The RVR is used to allow EGR and exhaust pressure regulator (EPR) valves to change position quickly as throttle position is changed.
A solenoid is placed between the RVR and VMV that blocks vacuum to the EGR valve whenever the torque converter clutch is applied.
V8 ENGINES
On V8 diesel engines, vacuum from the vacuum pump is modulated by the vacuum regulator valve (VRV) mounted on the injection pump. Vacuum is highest at idle and decreases to zero at wide open throttle. The EGR valve is therefore fully open at idle and closed at wide open throttle.
A response vacuum reducer (RVR) is used between the VRV and EGR valves to allow EGR valve to change position quickly as throttle position is changed. A solenoid in the system shuts off vacuum to the EGR valve when the torque converter clutch (TCC) is engaged.
EGR Valve Mounting Location (V6 & V8 Diesel Engine). Scheme 76
EGR System Vacuum Diagram (V6 Diesel). Scheme 77
EGR System Vacuum Diagram (V8 Diesel). Scheme 78
VACUUM REGULATOR VALVE (VRV)
- VRV regulates vacuum from vacuum pump in proportion to throttle angle. Vacuum from vacuum pump is supplied to port "A" and vacuum at port "B" is reduced as throttle is opened. (Scheme 79)
- Vacuum at port "B" should be 15 in. Hg at closed throttle, 6 in. Hg at half throttle and 0 in. Hg at wide open throttle.
Vacuum Regulator Valve (V6 & V8 Diesel Engines). Scheme 79
EXHAUST GAS RECIRCULATION (EGR) VALVE
- On V6 engines, gradually apply vacuum to vacuum port on EGR valve. EGR valve should be fully open at 12 in. Hg and closed below 7.5 in. Hg.
- On V8 engines, gradually apply vacuum to vacuum port on EGR valve. EGR valve should be fully open at 9.5-10.5 in. Hg and closed below 6 in. Hg.
- If either valve does not operate as described in steps 1) and 2), replace EGR valve.
RESPONSE VACUUM REDUCER (RVR)
- Connect a vacuum gauge to port marked "To VMV/VLV" on V6 engines or to port marked "To TCC Solenoid" on V8 engines. Connect a hand vacuum pump to VRV port.
- Apply 15 in. Hg of vacuum on pump. Vacuum gauge reading should be 12.5 in. Hg on High Altitude V8 engines and 14.25 in. Hg on all other models. If vacuum gauge readings are not as specified, replace RVR.
TORQUE CONVERTER CLUTCH (TCC) OPERATED SOLENOID
- When TCC is engaged, an electrical signal energizes solenoid allowing port 1 and 2 to be interconnected.
- When solenoid is not energized, port 1 is closed and ports 2 and 3 are interconnected.
VACUUM MODULATOR VALVE (VMV)
- Block drive wheels and apply parking brake. Place transmission in "P". Start engine and run at slow idle. Connect vacuum gauge to hose that connects to port marked "M".
- There should be at least 14 in. Hg of vacuum. If not, check vacuum pump, VRV, solenoid and connecting hoses.
- Reconnect vacuum hose to port "M". Connect vacuum gauge to port "D" on VMV. Vacuum reading should be 13 in. Hg. If not, replace VMV.