GM Corvette 1984-1996 Repair Guide

Exhaust Gas Recirculation System

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OPERATION



All models, except 1990-92 5.7L (VIN J) engines, are equipped with an EGR system, which consists of a metering valve and cast-in exhaust passages in the intake manifold. The EGR valve opens and closes in response to vacuum or electrical 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 two types of types of EGR systems used on these vehicles: Negative Backpressure and Linear. The principle of the two 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 vacuum control solenoid may sometimes be used in combination with the EGR valve. The 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.

Negative Backpressure Valve

See Figures 1 and 2

The negative backpressure EGR valve is used on 1984-96 5.7L (VIN 8, P and 5) engines.

This EGR valve varies the amount of exhaust gas flow into the intake manifold depending on manifold vacuum and variations in exhaust backpressure. An air bleed valve, located inside the EGR valve assembly acts as a vacuum regulator. The bleed valve controls the amount of vacuum in the vacuum chamber by bleeding vacuum to outside air during the open phase of the cycle. The diaphragm on the 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 spring. 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.



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Fig. Fig. 1: Negative backpressure EGR valve airflow schematic



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Fig. Fig. 2: Cross-sectional view of the negative backpressure EGR valve

Linear EGR System

See Figures 3 and 4

The 1990-92 5.7L (VIN J) engine does not use an EGR valve.

The linear EGR valve, used on 1993-95 5.7L (VIN J) engines, is designed to accurately supply EGR to an engine, 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. During operation, the PCM controls pintle position by monitoring the pintle position feedback signal. The PCM uses information from the Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor and the Mass Air Flow (MAF) sensor to determine the appropriate rate of flow for a particular engine operating condition.



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Fig. Fig. 3: Schematic of the linear EGR system air flow



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Fig. Fig. 4: Cross-sectional view of the linear EGR valve

TESTING



Negative Backpressure EGR Valve
  1. Inspect all passages and moving parts for plugging, sticking and deposits.
  2.  
  3. Inspect the entire system (hoses, tubes, connections, etc.) for leakage. Replace any part that is leaking, hardened, cracked, or melted.
  4.  
  5. Run the engine to normal operating temperature, and allow the engine to idle for 2 minutes. Quickly accelerate the engine to 2,500 rpm. Visible movement of the EGR stem should occur indicating proper system function. If no movement occurs, check the vacuum source and hose.
  6.  
  7. To determine if gas is flowing through the system, connect a vacuum pump to the valve.
  8.  
  9. With the engine idling, slowly apply vacuum. Engine speed should start to decrease when applied vacuum reaches 3 in. Hg. (10 kPa) The engine speed may drop quickly and could even stall; this indicates proper function.
  10.  
  11. If engine speed does not drop off, remove the EGR valve and check for plugged passages. If everything checks out, replace the valve.
  12.  

Linear EGR Valve

See Figures 5, 6 and 7

To check this system, refer to the accompanying diagnostic chart.



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Fig. Fig. 5: Linear EGR system schematic



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Fig. Fig. 6: Linear EGR system check-1 of 2



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Fig. Fig. 7: Linear EGR system check-2 of 2

REMOVAL & INSTALLATION



5.7L (VIN 8, P and 5) Engines

See Figures 8, 9 and 10

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. If necessary for access, either remove the intake plenum, or, remove the left fuel rail cover and disconnect the hose from the AIR check valve.
  6.  



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Fig. Fig. 8: On some vehicles it is necessary to remove the intake plenum to remove the EGR valve

  1. Disconnect the vacuum hose from the EGR valve.
  2.  
  3. Unfasten the retaining bolts, then remove the EGR valve from the manifold.
  4.  
  5. If the EGR passages show an excessive build up of deposits, you must clean the passages. Make sure all loose particles are completely removed to prevent them from clogging the EGR valve or being drawn into the engine. Clean the EGR passages as follows:
    1. Hold the valve in your hand. Tap on the end of the round pintle using a light snapping action with a plastic hammer. This will remove the exhaust deposits from the valve seal. Remove all of the loose particles.
    2.  
    3. Clean the mounting surface of the valve with a wire wheel or brush and the pintle with a wire brush.
    4.  
    5. Depress the valve diaphragm and check the seating area for cleanliness and signs of rubbing by looking through the valve outlet. If the pintle and/or seal aren't clean, repeat the 2 previous steps.
    6.  
    7. Hold the bottom of the valve securely and try to rotate the top of the valve back and forth. Replace the valve if any looseness is felt.
    8.  
    9. Check the valve for deposits. Remove any deposit build up with a suitable scraping tool.
    10.  

  6.  
  7. Clean the manifold mounting surface.
  8.  



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Fig. Fig. 9: Exploded view of the EGR valve mounting-1984 vehicle shown



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Fig. Fig. 10: Location of the EGR valve mounting-1995 vehicle shown

To install:
  1. Position a new gasket, then install the valve.
  2.  
  3. Install the retaining bolts and tighten to 16 ft. lbs. (22 Nm).
  4.  
  5. Connect the vacuum hose to the EGR valve.
  6.  
  7. If removed, connect the hose to the AIR check valve and install the left fuel rail cover.
  8.  
  9. If removed, install the intake plenum.
  10.  
  11. Install the air cleaner assembly.
  12.  
  13. Connect the negative battery cable.
  14.  

5.7L (VIN J) Engines

See Figure 11

  1. Disconnect the negative battery cable.
  2.  
  3. Raise and safely support the vehicle.
  4.  
  5. Remove the right side engine mount retaining nut.
  6.  
  7. Loosen the left side engine mount retaining nut.
  8.  
  9. Carefully lower the vehicle.
  10.  


WARNING
When raising the engine, do NOT use the catalytic converters as a lifting point, as this could damage the converters.

  1. Using a floor jack, with a piece of wood on the pad of the jack, position the jack under the oil pan on the right side of the engine. Raise the engine on the right side, only enough for sufficient clearance.
  2.  
  3. Detach the electrical connector from the EGR valve.
  4.  
  5. Unfasten the retaining bolts, then remove the EGR valve from the vehicle.
  6.  
  7. Thoroughly clean the gasket mating surfaces. If the EGR passages in the intake plenum and EGR base show an excessive deposit build up, you must clean the passages. Make sure all loose particles are completely removed to prevent them from clogging the EGR valve or being drawn into the engine. Clean the EGR passages as follows:
    1. With a wire wheel, buff the exhaust deposits from the mounting surface and around the valve.
    2.  
    3. Look for exhaust deposits in the valve outlet. Remove any deposit build up with a suitable scraping tool.
    4.  
    5. Clean the mounting surfaces of the EGR base and valve assembly.
    6.  

  8.  



Click image to see an enlarged view

Fig. Fig. 11: Linear EGR valve mounting and location

To install:
  1. Position a new gasket, then install the EGR valve. Install the retaining bolts and tighten to 16 ft. lbs. (22 Nm).
  2.  
  3. Attach the electrical connector to the EGR valve.
  4.  
  5. Slowly and carefully lower the engine.
  6.  
  7. Raise and safely support the vehicle.
  8.  
  9. Install the right side engine mount retaining nut. Tighten the left side engine mounting retaining nut.
  10.  
  11. Carefully lower the vehicle.
  12.  
  13. Connect the negative battery cable.
  14.  

EGR Control Solenoid
5.7L (VIN 8, P AND 5) ENGINE

See Figures 12, 13 and 14

On later models, it is also referred to as the EGR vacuum control signal solenoid valve.

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner.
  4.  
  5. If necessary, remove the intake plenum or left fuel rail cover as necessary.
  6.  
  7. Detach the electrical connector from the solenoid.
  8.  
  9. Disconnect the vacuum hoses.
  10.  
  11. Unfasten the retaining nut, then remove the solenoid.
  12.  



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Fig. Fig. 12: Exploded view of the EGR control solenoid mounting-1984 vehicle shown



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Fig. Fig. 13: EGR control solenoid location-1990 vehicle shown



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Fig. Fig. 14: EGR control signal solenoid valve location-1995 vehicle shown, others similar

To install:
  1. Install the solenoid and bracket. Install the retaining nut and tighten to 17 ft. lbs. (24 Nm).
  2.  
  3. Attach the vacuum hoses and electrical connector.
  4.  
  5. If removed, install the left fuel rail cover as necessary.
  6.  
  7. Install the air cleaner.
  8.  
  9. Connect the negative battery cable.
  10.  

EGR Valve Signal Modifier Module
5.7L (VIN J) ENGINE
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the intake plenum.
  4.  
  5. Detach the electrical connector.
  6.  
  7. Unfasten the retaining bolts, then remove the EGR valve signal modifier module.
  8.  

To install:
  1. Position the EGR valve signal modifier module and secure with the mounting bolts. Tighten to 18 inch lbs. (2 Nm).
  2.  
  3. Attach the electrical connector.
  4.  
  5. Install the intake plenum.
  6.  
  7. Connect the negative battery cable.
  8.  

 
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