GM Firebird 1982-1992 Repair Guide

Exhaust Gas Recirculation (EGR) System

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See Figures 1 through 16

OPERATION



All models are equipped with this system, which consists of a metering valve, a vacuum line to the carburetor or intake manifold, and cast-in exhaust passages in the intake manifold. The EGR valve is controlled by vacuum, which opens and closes in response to the vacuum signals to admit exhaust gases into the air/fuel mixture. The exhaust gases lower peak combustion temperatures, reducing the formation of NOx. The valve is closed at idle and wide open throttle, but is open between the two extreme positions.

There are actually four types of EGR systems: Ported, Positive Back-Pressure, Negative Backpressure and Digital. The principle of all the systems are the same; the only difference is in the method used to control how the EGR valve opens.

Too much EGR flow at idle, cruise or during cold operation may result in the engine stalling after cold start, the engine stalling at idle after deceleration, vehicle surge during cruise and rough idle. If the EGR valve is always open, the vehicle may not idle. Too little or no EGR flow allows combustion temperatures to rise, which could result in spark knock (detonation), engine overheating and/or emission test failure.

A Thermal Vacuum Switch (TVS) or vacuum control solenoid may sometimes be used in combination with the EGR valve. The TVS will close off vacuum during cold operation. A vacuum control solenoid uses Pulse Width Modulation (PWM) to turn the solenoid ON and OFF numerous times a second and varies the amount of ON time (pulse width) to vary the amount of ported vacuum supplied the EGR valve.

Ported Valve

In the ported system, the amount of exhaust gas admitted into the intake manifold depends on a ported vacuum signal. A ported vacuum signal is one taken from the carburetor above the throttle plates; thus, the vacuum signal (amount of vacuum) is dependent on how far the throttle plates are opened. When the throttle is closed (idle or deceleration) there is no vacuum signal. Thus, the EGR valve is closed, and no exhaust gas enters the intake manifold. As the throttle is opened, a vacuum is produced, which opens the EGR valve, admitting exhaust gas into the intake manifold.



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Fig. Fig. 1: Ported vacuum EGR valve

Positive Backpressure Valve

This valve operates the same as the ported, except, it has an internal air bleed that acts as a vacuum regulator. The bleed valve controls the amount of vacuum inside the vacuum chamber during operation. When the valve receives sufficient exhaust backpressure through the hollow shaft, it closes the bleed; at this point the EGR valve opens.

This valve will not open, with vacuum applied to it, while the engine is idling or stopped.



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Fig. Fig. 2: Positive backpressure EGR valve

Negative Backpressure Valve

This valve is similar to the positive backpressure type, except, the bleed valve spring is moved from above the diaphragm to below it. The bleed valve is normally closed.

At certain manifold pressures, the EGR valve will open. When the manifold vacuum combines with the negative exhaust backpressure, the bleed hole opens and the EGR valve closes.

This valve will open when vacuum is applied and the engine is not running.



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Fig. Fig. 3: Negative backpressure EGR valve

Digital EGR Valve

The digital EGR valve, used on 3.1L (VIN T) engines, is designed to control the flow of EGR independent of intake manifold vacuum. The valve controls EGR flow through 3 solenoid-opened orifices, which increase in size, to produce 7 possible combinations. When a solenoid is energized, the armature with attached shaft and swivel pintle, is lifted, opening the orifice.

The digital EGR valve is opened by the ECM "quad-driver'' (QDR), grounding each solenoid circuit individually. The flow of EGR is regulated by the ECM which uses information from the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS) and the Manifold Absolute Pressure (MAP) sensor to determine the appropriate rate of flow for a particular engine operating condition.



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Fig. Fig. 4: Digital EGR valve used on 3.1L engines



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Fig. Fig. 5: Thermostatic Vacuum Switch (TVS) controlled EGR system



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Fig. Fig. 6: Solenoid controlled EGR system

IDENTIFICATION





Positive backpressure EGR valves will have a "P'' stamped on the top side of the valve below the date built
 
Negative backpressure EGR valves will have a "N'' stamped on the top side of the valve below the date built
 
Port EGR valves have no identification stamped below the date built
 

SERVICE



  1. Check to see if the EGR valve diaphragm moves freely. Use your finger to reach up under the valve and push on the diaphragm. If it doesn't move freely, the valve should be replaced. The use of a mirror will aid the inspection process.
  2.  


CAUTION
If the engine is hot, wear a glove to protect your hand.

  1. Install a vacuum gauge into the vacuum line between the EGR valve and the vacuum source. Start the engine and allow it to reach operating temperature.
  2.  



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Fig. Fig. 7: Some EGR valves may be tested using a vacuum pump by watching for diaphragm movement

  1. With the car in either P or N , increase the engine speed until at least 5 in. Hg is showing on the gauge.
  2.  
  3. Remove the vacuum hose from the EGR valve. The diaphragm should move downward (valve closed). The engine speed should increase.
  4.  
  5. Install the vacuum hose and watch for the EGR valve to open (diaphragm moving upward). The engine speed should decrease to its former level, indicating exhaust recirculation.
  6.  
  7. If the diaphragm doesn't move, check engine vacuum; it should be at least 5 in. Hg with the throttle open and engine running.
  8.  
  9. Check to see that the engine is at normal operating temperature.
  10.  
  11. Check for vacuum at the EGR hose. If no vacuum is present, check the hose for leaks, breaks, kinks, improper connections, etc., and replace as necessary.
  12.  
  13. If the diaphragm moves, but the engine speed doesn't change, check the EGR passages in the intake manifold for blockage.
  14.  

REMOVAL & INSTALLATION



EGR Valve
EXCEPT 3.1L ENGINE
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly, if necessary.
  4.  

If equipped with the 5.0L (VIN F) and 5.7L (VIN 8) engines with Tuned Port Injection (TPI), it will be necessary to remove the intake plenum to gain access to the EGR valve.

  1. Tag and disconnect the necessary hoses and wiring to gain access to the EGR valve.
  2.  
  3. Remove the EGR valve retaining bolts.
  4.  
  5. Remove the EGR valve. Discard the gasket.
  6.  
  7. Buff the exhaust deposits from the mounting surface and around the valve using a wire wheel.
  8.  
  9. Remove deposits from the valve outlet.
  10.  
  11. Clean the mounting surfaces of the intake manifold and valve assembly.
  12.  

To install:
  1. Install a new EGR gasket.
  2.  
  3. Install the EGR valve to the manifold.
  4.  
  5. Install the retaining bolts.
  6.  
  7. Connect the wiring and hoses.
  8.  
  9. Install the air cleaner assembly.
  10.  
  11. Connect the negative battery cable.
  12.  



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Fig. Fig. 8: EGR valve control solenoid on 2.8L engines



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Fig. Fig. 9: EGR valve assembly on 2.8L engines



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Fig. Fig. 10: EGR valve assembly on 3.8L turbo engines



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Fig. Fig. 11: EGR valve location on carbureted and throttle body injected V8 engines



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Fig. Fig. 12: EGR valve and solenoid assembly on Tuned Port Injection engines

3.1L ENGINE
  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the electrical wiring at the solenoid.
  4.  
  5. Remove the 2 base-to-flange bolts.
  6.  
  7. Remove the digital EGR valve.
  8.  

To install:
  1. Install the gasket with "UP'' readable after positioning on the adapter.
  2.  
  3. Install the digital EGR valve.
  4.  
  5. Install the 2 base-to-flange bolts. Tighten the bolts to 11 ft. lbs (15 Nm) first, then torque to 22 ft. lbs. (30 Nm).
  6.  
  7. Connect the negative battery cable.
  8.  



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Fig. Fig. 13: Digital EGR valve assembly

EGR Solenoid
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner, as required.
  4.  
  5. Disconnect the electrical wiring 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. Connect the electrical wiring.
  8.  
  9. If removed, install the air cleaner.
  10.  
  11. Connect the negative battery cable.
  12.  



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Fig. Fig. 14: Disconnect and label the EGR valve vacuum hose



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Fig. Fig. 15: Removing the EGR valve from the engine



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Fig. Fig. 16: Discard the old gasket. Be sure the remove all carbon deposits from the ports on the EGR valve and the mounting surface

 
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