GM Astro/Safari 1985-1996 Repair Guide

Exhaust Gas Recirculation (EGR)

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OPERATION



See Figures 1, 2, 3, 4, 5, 6, 7 and 8



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Fig. Fig. 1: EGR valve identification



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Fig. Fig. 2: Linear EGR valve identification



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Fig. Fig. 3: Flow diagram of the EGR valve



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Fig. Fig. 4: Cutaway drawing of a negative pack pressure EGR valve



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Fig. Fig. 5: Cutaway drawing of a linear EGR valve



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Fig. Fig. 6: EGR system controlled by TVS



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Fig. Fig. 7: EGR system controlled by solenoid valve and ECM



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Fig. Fig. 8: EGR control solenoid

The EGR system's purpose is to control oxides of nitrogen which are formed during the peak combustion temperatures. The end products of combustion are relatively inert gases derived from the exhaust gases which are directed into the EGR valve to help lower peak combustion temperatures.

The port EGR valve is controlled by a flexible diaphragm which is spring loaded to hold the valve closed. Vacuum applied to the top side of the diaphragm overcomes the spring pressure and opens the valve which allows exhaust gas to be pulled into the intake manifold and enter the engine cylinders.

The negative backpressure EGR valve has a bleed valve spring below the diaphragm, and the valve is normally closed. The valve varies the amount of exhaust flow into the manifold depending on manifold vacuum and variations in exhaust backpressure.

The diaphragm on this valve has an internal air bleed hole which is held closed by a small spring when there is no exhaust backpressure. Engine vacuum opens the EGR valve against the pressure of a large. When manifold vacuum combines with negative exhaust backpressure, the vacuum bleed hole opens and the EGR valve closes. This valve will open if vacuum is applied with the engine not running.

The linear EGR valve is operated exclusively by the control module command. The control module monitors various engine parameters:



Throttle Position Sensor (TPS)
 
Manifold Absolute Pressure (MAP)
 
Engine Coolant Temperature (ECT) sensor
 
Pintle position sensor
 

Output messages are then sent to the EGR system indicating the proper amount of exhaust gas recirculation necessary to lower combustion temperatures.

TESTING



EGR Valve
NEGATIVE BACKPRESSURE EGR VALVE
  1. Remove the vacuum hose from the EGR valve.
  2.  
  3. Using a vacuum source, connect it to the EGR valve hose fitting and apply 10 in. Hg (33.8 kPa); the valve should lift off of its seat. If not, replace the EGR valve.
  4.  
  5. Clean the carbon deposits from the valve and intake manifold. With the valve removed, run the engine for 3-5 seconds to blow the carbon out of the intake manifold.
  6.  

LINEAR EGR VALVE

See Figures 9 and 10



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Fig. Fig. 9: Linear EGR valve pinouts-with CMFI/CSFI



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Fig. Fig. 10: Linear EGR valve pinouts-with TBI

  1. Remove the electrical connector from the EGR valve.
  2.  
  3. Measure the resistance between terminals A and E.
  4.  
  5. The resistance should be 9.5-10.5 ohms. Replace the valve if that is not correct
  6.  
  7. Remove the EGR valve from the engine.
  8.  
  9. Measure the resistance between terminals B and C while moving the pintle in and out. The resistance should change in a smooth fashion without skips or jumps. Replace if necessary.
  10.  

EGR Control Solenoid
  1. Disconnect the electrical connector from the solenoid.
  2.  
  3. Using an ohmmeter, measure the solenoid's resistance, it should be more than 20 ohms. If less than 20 ohms, replace the solenoid and/or possibly the ECM.
  4.  

Thermostatic Vacuum Switch

If the thermostatic vacuum switch is not working, a Code 32 will store in the ECM memory and a "Service Engine Soon'' lamp will light on the instrument panel.

  1. Remove the TVS from the engine.
  2.  
  3. Using a vacuum gauge, connect it to one of the hose connections and apply 10 in. Hg (33.8 kPa).
  4.  

A vacuum drop of 2 in. Hg (6.7 kPa) in 2 minutes is allowable.

  1. Place the tip of the switch in boiling water. When the switch reaches 195°F (91°C), the valve should open and the vacuum will drop; if not, replace the switch.
  2.  

REMOVAL & INSTALLATION



EGR Valve

See Figures 11, 12, 13, 14, 15, 16, 17 and 18



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Fig. Fig. 11: EGR mounting-2.5L engine



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Fig. Fig. 12: EGR mounting-4.3L TBI engine



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Fig. Fig. 13: EGR mounting-4.3L CMFI engine



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Fig. Fig. 14: EGR mounting-4.3L CSFI engine



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Fig. Fig. 15: Disconnect the vacuum hose and tag it for identification



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Fig. Fig. 16: A distributor wrench makes accessing the mounting hardware much easier



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Fig. Fig. 17: Pull the EGR valve away along with the old gasket



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Fig. Fig. 18: Always use a new gasket when installing. Notice that this one is burned in the center

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly or air inlet duct from the engine.
  4.  
  5. Remove the EGR valve vacuum tube from the valve, except for the linear EGR valves from which the electrical plug is disconnected.
  6.  
  7. Remove the EGR bolts and/or nuts and remove the EGR valve and gasket.
  8.  

To install:
  1. Install a new gasket to the EGR valve and install the EGR valve to the manifold.
  2.  
  3. Install the nuts and/or bolts. Tighten the bolts to 17-18 ft. lbs. (24-25 Nm) and/or the nuts to 15 ft. lbs. (20 Nm).
  4.  
  5. Connect the vacuum tube or electrical plug to the EGR valve.
  6.  
  7. Install the air cleaner or air duct and connect the negative battery cable.
  8.  

EGR Solenoid

See Figures 19, 20, 21 and 22



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Fig. Fig. 19: EGR and TVS connections-4.3L carbureted engine



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Fig. Fig. 20: EGR valve and solenoid-4.3L carbureted engine



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Fig. Fig. 21: EGR valve and solenoid-2.5L engine



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Fig. Fig. 22: EGR valve and solenoid-4.3L TBI engine

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner, as required.
  4.  
  5. Unplug the electrical connector at the solenoid.
  6.  
  7. Disconnect the vacuum hoses.
  8.  
  9. Remove the retaining bolts and the solenoid.
  10.  
  11. Remove the filter, as required.
  12.  

To install:
  1. If removed, install the filter.
  2.  
  3. Install the solenoid and retaining bolts.
  4.  
  5. Connect the vacuum hoses.
  6.  
  7. Engage the electrical connector.
  8.  
  9. If removed, install the air cleaner.
  10.  
  11. Connect the negative battery cable.
  12.  

 
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