GM Lumina/Silhouette/Transport APVs 1990-1999 Repair Guide

Exhaust Gas Recirculation System

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OPERATION



The EGR system is used to lower NOx (oxides of nitrogen) emission levels caused by high combustion temperatures. The main element of the system is the EGR valve The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. This dilutes the air/fuel mixture and consequently reduces combustion temperatures.

The EGR valve used on the 3.1L (VIN D) engine is a negative backpressure valve. It varies the amount of exhaust gas flow into the manifold depending on manifold vacuum and variations in exhaust backpressure. The diaphragm on this EGR valve has an internal vacuum bleed hole that is held closed by a small spring when there is no exhaust backpressure. The amount of vacuum to the valve is controlled buy a PCM controlled solenoid valve, called an Electronic Vacuum Regulator Valve (EVRV).

The linear EGR valve, used on the 3.8L and the 3.4L engine, is designed to accurately supply the engine with an EGR flow independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through an orifice with a PCM controlled pintle. PCM control means the EGR valve is usually activated when the engine is warm and operating above idle speed.

COMPONENT TESTING



Incorrect operation of the EGR system causing too much EGR flow at idle, cruise, or cold operation can cause any of the following condition to occur:



Engine stalls after a cold start.
 
Engine stalls at idle after deceleration.
 
Vehicle surges at a steady cruise.
 
Vehicle exhibits a rough idle.
 

The EGR valve should always be closed at wide-open throttle and idle.

See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Linear EGR test procedure shown

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause:



Spark knock (pinging), and if carried to the extreme, detonation.
 
The engine to overheat.
 
Emission test failure.
 

Removal & Installation



  1. Disconnect the negative battery cable.
  2.  
  3. If equipped, detach the electrical connector at the solenoid.
  4.  
  5. Remove the two base to flange nuts and lift the EGR valve assembly from its mount.
  6.  

To install:

See Figure 2

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of the Linear EGR Valve-other model is similar

  1. Thoroughly clean the gasket mounting surfaces. Replace the gasket.
  2.  
  3. Install the EGR assembly, install the two nuts and tighten to 22 ft. lbs. (30Nm).
  4.  
  5. If necessary, attach the electrical connector.
  6.  
  7. Connect the negative battery cable.
  8.  

See Figures 3 through 7

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Fig. Fig. 3: Typical EGR Valve installation and location for 3.8L engine



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Fig. Fig. 4: EGR Valve with electrical connector removed



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Fig. Fig. 5: Remove the two retaining bolts for the EGR valve



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Fig. Fig. 6: Remove the EGR valve



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Fig. Fig. 7: Removing and checking the gasket

 
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