GM Camaro/Firebird 1993-1998 Repair Guide

Exhaust Gas Recirculation (EGR) System Repair Guide

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OPERATION



See Figure 1

All models 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 three types of types of EGR systems used on these vehicles: Digital, Negative Backpressure and Linear. 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 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.



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Fig. Fig. 1: Solenoid controlled EGR system

Digital EGR Valve

See Figure 2

The digital EGR valve, used on the 3.4L engine, 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.



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Fig. Fig. 2: Exploded view of the digital EGR valve, used on the 3.4L engine

The digital EGR valve is opened by the PCM "Quad-Driver'' (QDR), grounding each solenoid circuit individually. The flow of EGR is regulated by the PCM 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.

Negative Backpressure Valve

See Figures 3 and 4

The negative backpressure EGR valve is used on the 1993-97 5.7L 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. 3: The 1993-97 5.7L engine uses a negative backpressure EGR valve



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

Linear EGR System

See Figures 5, 6 and 7

The linear EGR valve, used on 3.8L and 1998 5.7L 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. 5: The 3.8L and 1998 5.7L engines are equipped with a linear EGR valve



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Fig. Fig. 6: Cross-sectional view of the linear EGR valve



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Fig. Fig. 7: Schematic of the linear EGR system air flow

TESTING



Digital EGR Valve

This system must be checked using a Tech 1® or equivalent scan tool. Steps 4, 5 and 6 must be done very quickly, as the PCM will adjust the idle air control valve to compensate for idle speed.

  1. Using a Tech 1® or equivalent scan tool, check for any diagnostic trouble codes and solve those problems first. Refer to the Diagnostic Trouble Code (DTC) lists later in this section.
  2.  
  3. Select "EGR CONTROL'' on the scan tool.
  4.  
  5. Start and run the engine, until it reaches normal operating temperature, then allow the engine to idle for 2 minutes.
  6.  
  7. Energize EGR SOL #1; engine rpm should drop slightly.
  8.  
  9. Energize EGR SOL #2; the engine should have a rough idle.
  10.  
  11. Energize EGR SOL #3; the engine should idle rough or stall.
  12.  
  13. If all tests were as specified, the system is functioning properly.
  14.  
  15. If not, check the EGR valve, pipe, adapter, gaskets, fittings, and all passages for damage, leakage or plugging. If all is OK, replace the EGR valve assembly.
  16.  

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 Figure 8

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



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Fig. Fig. 8: Linear EGR system check

REMOVAL & INSTALLATION



EGR Valve
3.4L ENGINE

See Figure 9

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector from the solenoid.
  4.  
  5. Remove the 2 base-to-flange bolts, then remove the digital EGR valve. Remove and discard the gasket.
  6.  
  7. Clean the EGR valve gasket mating surfaces.
  8.  



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Fig. Fig. 9: Exploded view of the EGR valve mounting-3.4L engine

To install:
  1. Install the gasket with "UP'' readable after positioning on the adapter.
  2.  
  3. Position the digital EGR valve.
  4.  
  5. Install the 2 base-to-flange bolts finger-tighten.
  6.  
  7. Tighten the bolts in two steps, first to 11 ft. lbs. (15 Nm), then to 22 ft. lbs. (30 Nm).
  8.  
  9. Attach the electrical connector to the solenoid.
  10.  
  11. Connect the negative battery cable.
  12.  

1993-97 5.7L ENGINE

See Figure 10

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the vacuum line from the EGR valve.
  4.  
  5. Unfasten the retaining nuts, then remove the EGR valve from the vehicle. Remove and discard the gasket.
  6.  
  7. Clean the EGR valve gasket mating surfaces.
  8.  



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Fig. Fig. 10: Negative backpressure EGR valve mounting-1993-97 5.7L engine

To install:
  1. Position a new gasket, then install the EGR valve on top of the gasket.
  2.  
  3. Install the retaining bolts and tighten to 16 ft. lbs. (22 Nm).
  4.  
  5. Attach the vacuum hose to the EGR valve.
  6.  
  7. Connect the negative battery cable.
  8.  

3.8L ENGINE

See Figure 11 and 12

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector from the EGR valve.
  4.  



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Fig. Fig. 11: Detach the electrical connector from the linear EGR valve

  1. Unfasten the 2 base-to-flange nuts, then remove the linear EGR valve. Remove and discard the gasket.
  2.  
  3. Clean the EGR valve gasket mating surfaces.
  4.  



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Fig. Fig. 12: Linear EGR valve location and mounting-3.8L engine

To install:
  1. Install a new EGR valve gasket.
  2.  
  3. Position the EGR valve, then hand-start the retaining nuts. Tighten the nuts to 22 ft. lbs. (30 Nm).
  4.  
  5. Attach the electrical connector to the EGR valve, then connect the negative battery cable.
  6.  

1998 5.7L ENGINE

See Figure 13

Make sure to carefully note the installed position of the EGR valve. Do NOT rotate the EGR valve 180 °.

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector.
  4.  
  5. Remove the valve-to-flange retaining bolts.
  6.  


WARNING
The EGR valve is an electrical component. Do not soak the valve is cleaner or solvent or the valve will be damaged.

  1. Remove the linear EGR valve and flange gasket.
  2.  
  3. Clean the EGR valve gasket mating surfaces.
  4.  



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Fig. Fig. 13: Exploded view of the linear EGR valve mounting-1998 5.7L engine

To install:
  1. Install a new flange gasket.
  2.  
  3. Position the EGR valve and secure with the mounting bolts. Tighten to bolts in two steps, first to 89 inch lbs., then to 18 ft. lbs. (25 Nm).
  4.  
  5. Attach the electrical connector.
  6.  
  7. Connect the negative battery cable.
  8.  

EGR Solenoid Valve

See Figure 14

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connector from the solenoid valve.
  4.  
  5. Tag and disconnect the vacuum hoses.
  6.  
  7. Remove the retaining bolts or nut, then remove the solenoid.
  8.  
  9. Remove the filter, as required.
  10.  



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Fig. Fig. 14: Exploded view of the EGR vacuum control signal solenoid valve-5.7L (VIN P) engine shown

To install:
  1. If removed, install the filter.
  2.  
  3. Install the solenoid and retaining bolts or nut.
  4.  
  5. Connect the vacuum hoses, as tagged during removal.
  6.  
  7. Attach the electrical connector.
  8.  
  9. Connect the negative battery cable.
  10.  

EGR Pipe
1998 5.7L ENGINES ONLY

See Figure 15

  1. Disconnect the negative battery cable.
  2.  
  3. Remove the EGR valve.
  4.  
  5. Remove the EGR pipe-to-intake manifold bolts and the EGR pipe-to-exhaust manifold bolts.
  6.  
  7. Remove the EGR pipe mounting bolts from the right cylinder head.
  8.  
  9. Remove the EGR pipe from the vehicle.
  10.  



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Fig. Fig. 15: The 1998 5.7L engine is equipped with an EGR pipe

To install:
  1. Position the EGR pipe.
  2.  
  3. Install the EGR pipe bolts to the right cylinder head.
  4.  
  5. Install the EGR pipe-to-exhaust manifold bolts and the EGR pipe-to-intake manifold bolts.
  6.  
  7. Install the EGR valve.
  8.  
  9. Connect the negative battery cable.
  10.  

 
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