GM Full Size Vans 1987-1997 Repair Guide

Exhaust Gas Recirculation (EGR)

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OPERATION



To lower the formation of nitrogen oxides (NOx) in the exhaust, it is necessary to reduce combustion temperatures. This is done in the diesel, as in the gasoline engine, by introducing exhaust gases into the cylinders through the EGR valve.

The Exhaust Pressure Regulator (EPR) valve and solenoid operate in conjunction with the EGR valve. The EPR valve's job is to increase exhaust backpressure in order to increase EGR flow. The EPR valve is usually open, and the solenoid is normally closed. When energized by the B+ wire from the Throttle Position Switch (TPS), the solenoid opens, allowing vacuum to the EPR valve, closing it. This occurs at idle. As the throttle is opened, at a calibrated throttle angle, the TPS de-energizes the EPR solenoid, cutting off vacuum to the EPR valve, closing the valve. Two other solenoids are used for EGR valve control. The EGR solenoid allows vacuum to reach the EGR vent solenoid under certain conditions. The vent solenoid then controls the EGR valve to regulate the flow of gasses into the intake manifold.

TESTING



Exhaust Gas Recirculation (EGR) Valve

Apply vacuum to the EGR valve with a hand vacuum pump. The valve should be fully open at 11 in. Hg and closed below 6 in. Hg.

EPR Valve
  1. Apply 11 in. Hg vacuum to the EPR valve tube with a hand vacuum pump. Observe the valve actuator lever for movement.
  2.  
  3. If it does not move, spray a penetrating lubricant on the lever and try to free the valve.
  4.  


CAUTION
Make sure the valve is not hot.

  1. If the lubricant will not free the valve, it must be replaced.
  2.  

Vacuum Regulator Valve (VRV)

The Vacuum Regulator Valve is attached to the side of the injection pump and regulates vacuum in proportion to throttle angle. Vacuum from the vacuum pump is supplied to port A and vacuum at port B is reduced as the throttle is opened. At closed throttle, the vacuum is 15 in.; at half throttle, 6 in.; at wide open throttle there is zero vacuum.

Response Vacuum Reducer (RVR)

Connect a vacuum gauge to the port marked To EGR valve to T.C.C. solenoid. Connect a hand operated vacuum pump to the VRV port. Draw a 50.66 kPa (15 in. Hg) vacuum on the pump and the reading on the vacuum gauge should be lower than the vacuum pump reading as follows:



0.75 in. Except High Altitude
 
2.5 in. High Altitude
 

Torque Converter Clutch Operated Solenoid

When the torque converter clutch is engaged, an electrical signal energizes the solenoid allowing ports 1 and 2 to be interconnected. When the solenoid is not energized, port 1 is closed and ports 2 and 3 are interconnected.

Solenoid Energized


Ports 1 and 3 are connected.
 

Solenoid De-Energized


Ports 2 and 3 are connected.
 

Vacuum Pump Diesel Engines

Since the air crossover and intake manifold in a diesel engine is unrestricted (unlike a gasoline engine which has throttle plates creating a venturi effect) there is no vacuum source. To provide vacuum, a vacuum pump is mounted in the location occupied by the distributor in a gasoline engine. This pump supplies the air conditioning servos, the cruise control servos, and the transmission vacuum modulator where required.

The pump is a diaphragm type which needs no maintenance. It is driven by a drive gear on its lower end which meshes with gear teeth on the end of the engine's camshaft.

REMOVAL & INSTALLATION



  1. Disconnect the batteries.
  2.  
  3. Remove the air cleaner, and cover the intake manifold.
  4.  
  5. Remove the vacuum pump clamp, disconnect the vacuum line and remove the pump.
  6.  
  7. Install a new gasket. Install the pump and reverse the removal procedures for installation.
  8.  

REMOVAL & INSTALLATION



EGR Valve

See Figure 1

  1. Remove the air cleaner assembly and air intake tube.
  2.  
  3. Unplug the vacuum hose from the valve.
  4.  
  5. Remove the studs securing the valve to the intake manifold.
  6.  
  7. Installation is the reverse of removal. Tighten the studs until snug.
  8.  



Click image to see an enlarged view

Fig. Fig. 1: EGR valve mounting

EPR Valve

See Figure 2

  1. Raise and safely support the vehicle.
  2.  
  3. Unplug the vacuum hose from the actuator.
  4.  
  5. Disconnect the exhaust pipe from the valve.
  6.  
  7. Remove the studs securing the valve to the exhaust manifold.
  8.  
  9. Installation is the reverse of removal.
  10.  

EGR/EPR Solenoid Assembly

See Figure 3

  1. Disconnect the negative battery cable.
  2.  
  3. Label and disconnect the vacuum hoses from the assembly.
  4.  
  5. Unplug the solenoid electrical connectors.
  6.  
  7. Remove the retainers securing the assembly to the intake manifold.
  8.  
  9. Installation is the reverse of removal.
  10.  



Click image to see an enlarged view

Fig. Fig. 2: EPR valve



Click image to see an enlarged view

Fig. Fig. 3: EGR/EPR solenoid assembly

 
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