GM Caprice 1990-1993 Repair Guide

Exhaust Gas Recirculation (EGR) System

Print

See Figures 1 through 6



Click image to see an enlarged view

Fig. Fig. 1: Positive backpressure EGR valve



Click image to see an enlarged view

Fig. Fig. 2: Vacuum operated EGR valve



Click image to see an enlarged view

Fig. Fig. 3: Negative backpressure EGR valve



Click image to see an enlarged view

Fig. Fig. 4: EGR control solenoid - 5.0L (VIN E) & 5.7L engine



Click image to see an enlarged view

Fig. Fig. 5: Electronic controlled EGR system - 5.0L (VIN Y) engine



Click image to see an enlarged view

Fig. Fig. 6: EGR identification

OPERATIONS



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

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.

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 back-pressure 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.

Negative Backpressure Valve

This valve is similar to the Positive 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.

INCORRECT EGR OPERATION



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 get too high which could result in spark knock (detonation), engine overheating and/or emission test failure.

EGR VALVE 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.
 

Additional Controls
EGR VACUUM/SOLENOID CONTROL

Some systems use the coolant temperature sensor, throttle position sensor and manifold air temperature sensor with the EGR valve. The EGR control solenoid uses a Pulse Width Modulation system which turns 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.

TESTING



EGR Valve

See Figures 7 through 14

The following charts may be used to diagnose EGR system malfunctions.



Click image to see an enlarged view

Fig. Fig. 7: EGR system testing - except 5.0L (VIN Y) engine



Click image to see an enlarged view

Fig. Fig. 8: EGR system testing - except 5.0L (VIN Y) engine, continued



Click image to see an enlarged view

Fig. Fig. 9: EGR system testing - except 5.0L (VIN Y) engine, continued



Click image to see an enlarged view

Fig. Fig. 10: EGR system testing - except 5.0L (VIN Y) engine, continued



Click image to see an enlarged view

Fig. Fig. 11: EGR system testing - except 5.0L (VIN Y) engine, continued



Click image to see an enlarged view

Fig. Fig. 12: EGR system testing - except 5.0L (VIN Y) engine, continued



Click image to see an enlarged view

Fig. Fig. 13: EGR system testing - 5.0L (VIN Y) engine



Click image to see an enlarged view

Fig. Fig. 14: EGR system testing - 5.0L (VIN Y) engine, continued

REMOVAL & INSTALLATION



EGR Valve
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Tag and disconnect the necessary hoses and wiring to gain access to the EGR valve.
  6.  
  7. Remove the EGR valve retaining bolts.
  8.  
  9. Remove the EGR valve. Discard the gasket.
  10.  
  11. Buff the exhaust deposits from the mounting surface and around the valve using a wire wheel.
  12.  
  13. Remove deposits from the valve outlet.
  14.  
  15. Clean the mounting surfaces of the intake manifold and valve assembly.
  16.  

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.  

EGR Solenoid
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner, as required.
  4.  
  5. Disconnect the electrical connector at the solenoid.
  6.  
  7. Disconnect the spark plug wires and vacuum hoses, as required.
  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 connector.
  8.  
  9. If removed, install the air cleaner.
  10.  
  11. Connect the negative battery cable.
  12.  

 
label.common.footer.alt.autozoneLogo