GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Exhaust Gas Recirculation System

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OPERATION



See Figures 1, 2 and 3

The 2.3L and 3.3L engines do not use an EGR valve.

The EGR system is used to reduce oxides of nitrogen (NOx) emission levels caused by high combustion chamber temperatures. This is accomplished by the use of an EGR valve which opens, under specific engine operating conditions, to admit a small amount of exhaust gas into the intake manifold, below the throttle plate. The exhaust gas mixes with the incoming air charge and displaces a portion of the oxygen in the air/fuel mixture entering the combustion chamber. The exhaust gas does not support combustion of the air/fuel mixture but it takes up volume, the net effect of which is to lower the temperature of the combustion process. This lower temperature also helps control detonation.



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Fig. Fig. 1: Exhaust Gas Recirculation (EGR) system flow



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Fig. Fig. 2: Ported and negative back pressure EGR valve identification

The EGR valve is a mounted on the intake manifold and has an opening into the exhaust manifold. The EGR valve is opened by ported vacuum and allows exhaust gases to flow into the intake manifold. If too much exhaust gas enters, combustion will not occur. Because of this, very little exhaust gas is allowed to pass through the valve. The EGR system will be activated once the engine reaches normal operating temperature and the EGR valve will open when engine operating conditions are above idle speed and below Wide Open Throttle (WOT). On California vehicles equipped with a Vehicle Speed Sensor (VSS), the EGR valve opens when the VSS signal is greater than 2 mph. The EGR system is deactivated on vehicles equipped with a Transmission Converter Clutch (TCC) when the TCC is engaged.



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Fig. Fig. 3: Exploded view of the digital EGR valve which is used on the 3.1L engine

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.

The four types of EGR valves used on N body vehicles are ported, negative backpressure and digital; they differ mainly in the way EGR flow is modulated.

Ported EGR Valve

The ported EGR valve, used on the 2.0L and 3.0L engines, takes its name from the fact that it uses a ported vacuum source to open the EGR valve and modulate the EGR flow. The ported vacuum source is a small opening just above the throttle blade in the throttle body. When the throttle begins to open the air passing through the venturi, creates a low pressure which draws on the EGR valve diaphragm causing it to open. As the throttle blade opens further, the ported vacuum increases and opens the valve further.

The ECM controls EGR operation through an EGR control solenoid. Ported vacuum must flow through the EGR control solenoid to open the EGR valve. The ECM uses information received from the Coolant Temperature Sensor (CTS), Throttle Position Sensor (TPS) and the Mass Air Flow (MAF) sensor to determine when to allow EGR operation. When certain parameters are met, such as engine at normal operating temperature and the engine speed is above idle, the ECM signals the solenoid to open, allowing EGR operation.

Negative Backpressure EGR Valve

The negative backpressure EGR valve, used on the 2.5L engine, varies the amount of exhaust gas flow into the intake manifold depending on manifold vacuum and variations in exhaust backpressure. Like the ported EGR valve, the negative backpressure EGR valve uses a ported vacuum source. 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.

Digital EGR Valve

The digital EGR valve, used on the 3.3L engine, and 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 three orifices which increment in size to produce seven combinations. When a solenoid is energized, the armature, with attached shaft and swivel pintle is lifted, opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.

The swivel pintle feature insures good sealing of exhaust gas, reducing the need of critical assembly alignment. In addition, the effects of EGR leakage on idle quality are reduced because the shaft and seals are exposed to exhaust pressure instead of manifold vacuum. The shafts are sealed from the exhaust chamber by floating seals held in place by the seal spring. These springs also hold the upper seals that seal the armature cavity in the solenoids. The solenoid coils are fastened together to maximize reliability and to seal the coils from the environment. The coils use a common power terminal with individual ground terminals.

The digital EGR valve is opened by the PCM quad-driver, grounding each respective solenoid circuit. This quad-driver activates the solenoid, raises the pintle, and allows exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve, with virtually none at idle.

Linear EGR Valve

The linear EGR valve is used on the 2.4L and 3.1L engines. The valve is designed to accurately supply EGR to an engine independent of the 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 feedback signal can be monitored with a scan tool as actual EGR position. Actual EGR position should always be near the commanded EGR position (desired EGR position). If a problem occurs with the EGR system, the system will not allow the PCM to control the pintle position properly. A code will set. The PCM also tests for EGR flow; if the incorrect flow is detected, the code should set. If the code is encountered, refer to the tables at the end of this section.

The linear EGR valve is usually activated under the following conditions:



Warm engine operation
 
Above idle speed
 

The PCM monitors the EGR actual position and adjusts pintle position accordingly. The PCM uses information from the following sensors to control the pintle position:



Engine Coolant Temperature (ECT) Sensor
 
Throttle Position (TP) Sensor
 
Mass Air Flow (MAF) Sensor
 

TESTING



See Figures 4 through 8

Refer to the appropriate chart to test the EGR system.



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Fig. Fig. 4: Ported EGR system check



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Fig. Fig. 5: Negative backpressure EGR system check



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Fig. Fig. 6: Digital EGR system check



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Fig. Fig. 7: Linear EGR system check



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Fig. Fig. 8: Linear EGR system check (page 2)

REMOVAL & INSTALLATION



Ported and Negative Backpressure EGR Valves

See Figures 9, 10, 11 and 12

  1. Disconnect the negative battery cable.
  2.  
  3. If necessary for valve access, remove the air cleaner assembly.
  4.  
  5. If equipped, remove the EGR valve cover.
  6.  



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Fig. Fig. 9: If equipped, remove the cover by lifting it off the valve

  1. Tag and disconnect the necessary EGR valve hoses and wiring.
  2.  



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Fig. Fig. 10: Disconnect the vacuum hose

  1. Unfasten the EGR valve retaining bolts.
  2.  



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Fig. Fig. 11: Unfasten the EGR retaining bolts or nuts ...

  1. Remove the EGR valve. Discard the gasket.
  2.  



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Fig. Fig. 12: ... and remove the EGR valve from the engine

  1. Buff the exhaust deposits from the mounting surface and around the valve using a wire wheel.
  2.  
  3. Remove deposits from the valve outlet.
  4.  
  5. Clean the gasket material from the mounting surfaces of the intake manifold and valve assembly.
  6.  

To install:
  1. Using a new gasket, position the EGR valve on the manifold.
  2.  
  3. Install the retaining bolts, then tighten them to 16 ft. lbs. (22 Nm).
  4.  
  5. Connect the wiring and hoses.
  6.  
  7. Place the cover on the valve, if equipped.
  8.  
  9. Install the air cleaner assembly.
  10.  
  11. Connect the negative battery cable.
  12.  

Digital EGR Valve

See Figure 13

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connections at the solenoid.
  4.  
  5. Unfasten the two base-to-pad retaining bolts/screws, then remove the EGR valve from the engine. Remove and discard the gasket.
  6.  
  7. Clean the gasket mating surfaces.
  8.  



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Fig. Fig. 13: View of the digital EGR valve mounting-3.1L engine

To install:
  1. Position a new EGR valve gasket, aligning it with the holes.
  2.  
  3. Install then bolts, aligning them through the EGR valve assembly and cast EGR pad of the upper intake manifold and into the pipe assembly. Tighten the bolts to 18 ft. lbs. (25 Nm).
  4.  
  5. Attach the electrical connections to the solenoid.
  6.  
  7. Connect the negative battery cable.
  8.  

Linear EGR Valve

See Figures 14 and 15

  1. If necessary, remove the air cleaner outlet resonator.
  2.  
  3. Detach the electrical wiring connected to the EGR vale.
  4.  



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Fig. Fig. 14: Linear EGR valve mounting-3.1L engine



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Fig. Fig. 15: Linear EGR valve mounting-2.4L engine

  1. Unbolt the valve and lift from the engine compartment.
  2.  
  3. Remove and discard the gasket.
  4.  

To install:
  1. Place a new gasket into position and seat the EGR valve. Secure the valve and tighten the nuts to 16-22 ft. lbs. (22-30 Nm).
  2.  
  3. Attach the wiring to the EGR valve.
  4.  
  5. Install the air cleaner resonator if removed.
  6.  

EGR Control Solenoid

See Figure 16

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the electrical connection and vacuum hoses at the solenoid.
  4.  
  5. Unfasten the retaining nut, then remove the solenoid.
  6.  



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Fig. Fig. 16: EGR control solenoid components

To install:
  1. Install the solenoid and bracket. Tighten the retaining nut to 17 ft. lbs. (24 Nm).
  2.  
  3. Attach the vacuum hoses and electrical connector.
  4.  
  5. Connect the negative battery cable.
  6.  

Filter Replacement

Grasp the filter and pull it off with a rocking motion. Install a new filter by pushing it on. Make sure the cut-outs for the wires are properly aligned.

 
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