EGR System - High Altitude: 1984 Vin T (4.3L) Diesel

Fig. 015 EGR System - High Altitude (Same as Fig. 50, p. 13-20):

VIN T HIGH ALTITUDE (NA6)

Vacuum from the vacuum pump is modulated by the Vacuum Regulator Valve mounted on the injection pump. Vacuum is highest at idle and decreases to 10 kPa ± 3 (3.0 Hg. ± .9) at wide-open throttle. This variable vacuum then is sent to port 3 of the Transaxle Converter Clutch solenoid (and port "S" of the transaxle vacuum modulator Quick Vacuum Response (QVR) valve, 440-T4 only).
A QVR is an equalizing valve that reacts quickly. When the vacuum applied to port "S" is constant or increasing, the vacuum output will be the same as the input. When the vacuum at port "S" drops, the vacuum on the output side is vented through the vent opening of the QVR until the vacuum is the same.
The Tranxaxle Converter Clutch (dump) solenoid prevents vacuum from passing though whenever the Transaxle Converter Clutch is engaged. When the solenoid is energized, any vacuum present beyond the solenoid is vented through the "vent" port (1) of the solenoid. When the solenoid is not energized, vacuum is applied to port 3 of the Altitude (TRIM) solenoid and port 3 of the Altitude Vacuum Reducer Valve.
The Altitude Solenoid is energized by the EGR Altitude Sensing Control switch at altitudes below 1219 meters (4,000 ft.). When it is energized, ports 2 and 3 are connected and port 1 is blocked. Therefore vacuum at ports 3 and 2 of the VRV are the same. This causes the vacuum at port 1 of the VRV to also be the same as the vacuum at ports 2 and 3.
When the solenoid is not energized, ports 3 and 2 of the solenoid are connected and port 1 is blocked. Because port 3 of the Altitude Solenoid is a vent, port 2 of the VRV is open to atmospheric pressure. Now the VRV will regulate. The vacuum at port 1 of the VRV will now have a vacuum output 8.44 kPa (2.5 Hg.) lower than at port 3 of the VRV.
From port 1 of the VRV, the vacuum is applied to port 3 of the EGR Thermostatic Vacuum Switch (EGR-TVS). The EGR-TVS is installed in a coolant passage of the intake manifold. It does two things; 1. its upper part is an electrical switch that energizes the HPCA and fast idle solenoid when coolant temperature is below 35°C (95°F). 2. its lower part is a vacuum switch that prevents vacuum from flowing to port 2 until 41°C ± 2° (105°F ± 3.6°) coolant temperature is reached. Below 35°C (95°F), vacuum cannot pass from port 3 to 2. Any vacuum that was present at port 2 is vented through port 1. Port 1 is blocked when ports 3 and 2 are connected.
Vacuum is then sent to the EGR-QVR. The EGR-QVR operates the same as the Transaxle Modulator QVR. The EGR-QVR will quickly equalize the vacuum present in the EGR valve when vacuum input to port "S" of the QVR drops. The EGR valve is a vacuum modulated type. It should be fully open at 40.5 kPa (12 Hg.) and closed below 25.3 kPa (7.5 Hg.). VIN T




1984 Calif. & 1985 Buick Electra, Cadillac Fleetwood, Brougham, DeVille & Oldsmobile Ninety-Eight

Refer to ``Diesel Electronic Control (DEC) System'' for description, diagnosis and testing of the EGR system for these models.