GM Cadillac Deville_Fleetwood_ELD_Seville 1990-1998

Exhaust Gas Recirculation System

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OPERATION



The Exhaust Gas Recirculation (EGR) system is used in an automotive engine to decrease the emission levels of oxides of nitrogen (NOx). NOx defines a group of chemical compounds containing nitrogen and varying amounts of oxygen that can have harmful environmental effects in large quantities.

NOx forms during the combustion process in amounts that is dependent on the concentration of oxygen in the combustion chamber and the duration that the combustion process temperatures exceed 1500°F. Decreased NOx levels are accomplished by reducing the peak combustion temperature through dilution of the incoming air/fuel charge with exhaust. During combustion, exhaust gas (largely non-reactive carbon dioxide and water vapor) acts to absorb a portion of the combustion energy, resulting in lower temperatures throughout the combustion process yielding lower amounts of NOx.

Desired amounts of EGR depend upon geometry of the combustion chamber and the operating condition of the engine. Extensive laboratory and vehicle tests are used to determine optimal EGR rates for all operating conditions. Too little EGR can yield high NOx, while too much EGR can disrupt combustion events.

COMPONENT TESTING



Early Model Engines

The EGR valve is opened by vacuum to allow exhaust gases to flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. The Powertrain Control Module (PCM) controls the vacuum to the EGR valve with a solenoid valve. A constant 12 volts is supplied to the positive terminal on the EGR valve. The vacuum supply to the EGR valve is regulated by the PCM controlling the EGR solenoid ground. The percentage that the PCM grounds the EGR solenoid is called the duty cycle. The duty cycle is the time the solenoid is on divided by the time it is off. A de-energized solenoid allows vacuum to pass to the EGR valve. A duty cycle of 100 percent will turn the EGR full off since the solenoid will be energized and not allow vacuum to pass to the valve. The EGR pulse width is regulated by the PCM depending on engine load conditions. When the engine is cold, within specified load range and above a specified rpm, the PCM sends 100 percent duty cycle to the solenoid and blocks vacuum to the EGR valve. When the engine is warm, the PCM sends a duty cycle to the solenoid to allow EGR.

These engine use a positive backpressure EGR valve, which requires exhaust backpressure (proportional to engine flow) to open and allow exhaust gas to flow into the intake manifold.

The PCM uses the following sensors to control the EGR solenoid:



Coolant Temperature (CTS)
 
Throttle Position (TPS)
 
Manifold Pressure (MAP)
 
Manifold Air Temperature (MAT)
 
Throttle Switch (ISC)
 
RPM data from the distributor reference pulses
 
Vehicle Speed Sensor (VSS)
 

Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stall. With too much EGR flow at idle, cruise speed or cold operation, any of the following conditions may occur:



Engine stalls after cold start
 
Engine stalls at idle after deceleration
 
Car surges during cruise
 
Rough idle
 

If the EGR valve should stay open due to a stuck open valve, the engine may not run.

Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. Any of the following conditions may occur:



Spark knock
 
Emission test failure
 



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Fig. Exhaust Gas Recirculation (EGR) system check-4.5L engine



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Fig. Exhaust Gas Recirculation (EGR) system check-4.5L engine



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Fig. Exhaust Gas Recirculation (EGR) system check-4.9L engine



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Fig. Exhaust Gas Recirculation (EGR) system check-4.9L engine

Later Model Engines

The Northstar 4.6L engine uses a computer controlled EGR valve to precisely regulate the amount of EGR delivered to the engine for all operating conditions. Exhaust gases are routed to the engine through a corrugated semi-flexible feed pipe (EGR valve pipe) which connects the crossover exhaust pipe to the crossover water pump housing.

In the crossover water pump housing, exhaust gases are precisely metered by the PCM controlled EGR valve, then cooled by the engine coolant and finally routed to the front and rear cylinder heads. A potential drawback with EGR is that with certain driving schedules, deposits can accumulate when hot exhaust gases are cooled. The Northstar system uses the crossover water pump housing as a cross-flow heat exchanger to cool exhaust gases in large easily cleaned passages to virtually eliminate any concern with deposit accumulation during the service life of the engine. This is done by having the cooling passages reduce EGR gasses below their deposit forming temperature prior to routing these gasses into the cylinder distribution channels.

In each cylinder bank, exhaust gases travel under the intake manifold along an irregular shaped sandwich passage made up of the aluminum alloy cylinder head and a non-metallic distribution plate. Engine vacuum acts to draw exhaust gases through outlets in the distribution plate where mixing with the incoming fuel/air charges for each cylinder occurs. Although the openings look small, the EGR valve pintle is the flow limiter in the system.

The EGR valve regulates the amount of exhaust gas fed to the engine. This mixture is dependent upon the height of the pintle above the orifice in the base of the valve. The EGR system is comprised of the following subassemblies:



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Fig. EGR component layout-4.6L engine



Bobbin and Coil (Solenoid) assembly
 
Armature Assembly
 
Base
 

The bobbin and coil (solenoid) assembly consists of one solenoid that is encapsulated to maximize reliability, seal coils from the environment and prevent movement of the coils and terminal. Inside the solenoid (bobbin and coil) assembly, is an armature assembly, consisting of a pintle and valve assembly, two seals, retaining washer, a seal spring, and armature spring and a bearing. The valve pintle shaft is sealed from the exhaust chamber by a bearing. In addition, an armature shield, held in place by a compression spring, deflects exhaust gas from the shaft and the armature. The base adapter and base plate make up the base assembly.

As mentioned above, the PCM controlled EGR valve regulates the amount of exhaust gas fed to the engine. This device offers more precise EGR flow metering than a backpressure or digital type valve and superior emission control and driveability. The PCM monitors the following sensors to control the linear EGR valve:



Coolant Temperature (CT) sensor
 
Throttle position (TP) sensor
 
Manifold Pressure (MAP) sensor
 
Throttle Switch (TS)
 
RPM data
 
Vehicle Speed Sensor (VSS)
 



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Fig. EGR system operation-4.6L engine



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Fig. Computer controlled EGR valve assembly

Output messages are then sent to the EGR system indicating the proper amount of exhaust gas recirculation necessary to lower combustion temperatures. The solenoid assembly is energized by 12 volt current that enters the valve through an electrical connector, then flows through the solenoid assembly to the PCM, and creates an electromagnetic field. This field causes the armature assembly to be pulled upward, lifting the pintle a variable amount off the base. The exhaust gas then flows from the exhaust manifold (through the orifice) to the cylinder distribution channels. The height of the pintle is read by the pintle position sensor, and the PCM closes the loop on the desired position versus the actual position read. Then, until the actual pintle position equals the desired pintle position, the PCM changes the pulse width modulated command to the solenoid. This results in improved flow accuracy. The EGR valve is unique in that the PCM continuously monitors pintle height and continuously corrects it in order to obtain accurate flow in a closed loop system. When the solenoid is de-energized, (PCM breaks the circuit), the pintle is sealed against the orifice, blocking exhaust flow to the cylinder distribution channels.

To regulate EGR flow to the engine, the PCM controls the solenoid to directly vary the pintle position relative to the closed valve position. The EGR valve contains a potentiometer type position sensor that provides a voltage proportional to pintle position. Pintle position is used by the PCM for closed loop control of the valve pintle position to follow commanded position, for diagnostics, and to correct fuel spark for EGR.

Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stall. With too much EGR flow at idle, cruise speed or cold operation, any of the following conditions may occur:



Engine stalls after cold start
 
Engine stalls at idle after deceleration
 
Car surges during cruise
 

If the EGR valve should stay open due to a stuck open valve, the engine may not run.

Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. Any of the following conditions may occur:



Spark knock
 
Emission test failure
 



Click image to see an enlarged view

Fig. Exhaust Gas Recirculation (EGR) system check-4.6L engine



Click image to see an enlarged view

Fig. Exhaust Gas Recirculation (EGR) system check-4.6L engine

REMOVAL & INSTALLATION



EGR Valve
4.5L And 4.9L Engines
  1. Disconnect the negative battery terminal.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Remove the vacuum valve at the EGR valve.
  6.  
  7. Remove the 2 EGR valve mounting bolts and the EGR valve from the engine.
  8.  
  9. Inspect the EGR passages in the intake manifold for deposits and clean as necessary.
  10.  

To install:

  1. Install the cleaned or replacement EGR valve onto the intake manifold using new gasket. Tighten the 2 mounting bolts to 14 ft. lbs. (18 Nm).
  2.  
  3. Install the vacuum hose to the valve.
  4.  
  5. Install the air cleaner assembly and connect the negative battery terminal.
  6.  



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Fig. Exhaust Gas Recirculation (EGR) valve-positive backpressure type



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Fig. Exhaust gas recirculation



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Fig. EGR vacuum house routing-4.5L and 4.9L engines



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Fig. EGR valve service-4.5L and 4.9L engines

4.6L Engine
  1. Detach the electrical connector from the solenoid.
  2.  
  3. Remove the fuel line bracket nut (if equipped).
  4.  
  5. Lift the fuel line bracket off the stud (if equipped).
  6.  
  7. Push the fuel line bracket away from the EGR valve base (if equipped).
  8.  
  9. Remove the mounting nuts and/or volts from the base (if equipped).
  10.  
  11. Pull the EGR valve off its mounting base.
    1. Inspect the EGR passages in the crossover water pump housing for deposits.
    2.  
    3. Clean the EGR passages as needed.
    4.  

  12.  
  13. Clean the mounting surface for the EGR.
  14.  

To install:

  1. Install the cleaned or replacement EGR valve using a new gasket.
  2.  
  3. Tighten the mounting nuts and/or bolts to 18 ft. lbs. (24 Nm).
  4.  
  5. Place the fuel line bracket onto the EGR valve stud (if equipped).
    1. Tighten the bracket nut to 14 ft. lbs. (19 Nm).
    2.  

  6.  
  7. Attach the electrical connector.
  8.  



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Fig. EGR valve service-4.6L engine



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Fig. Unplug the connector from the EGR valve



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Fig. Remove the EGR-to-intake manifold retaining bolts



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Fig. Removing the EGR valve and inspecting the mounting gasket

EGR Valve Pipe

NOTE
It may be necessary to remove the crossover exhaust pipe in order to facilitate EGR valve pipe removal from the engine.

  1. Remove the pipe mounting bolt at water pump bracket.
  2.  
  3. Raise and safely support the vehicle.
  4.  
  5. Remove the crossover exhaust pipe, if required.
  6.  
  7. Remove the pipe-mounting nut at the crossover exhaust pipe. Remove the EGR valve pipe from the vehicle.
  8.  

To install:

  1. Install the EGR valve pipe. Install the nut at the crossover exhaust pipe and tighten to 44 ft. lbs. (60 Nm). Install the crossover-exhaust pipe and related components, if removed.
  2.  
  3. Lower the vehicle. Install the bolts at the water pump housing and tighten to 18 ft. lbs. (24 Nm).
  4.  



Click image to see an enlarged view

Fig. EGR valve pipe service-4.6L engine

EGR Control Solenoid
  1. Disconnect the negative battery cable.
  2.  
  3. Remove the air cleaner assembly.
  4.  
  5. Detach the electrical connector and the vacuum hoses at the EGR solenoid.
  6.  
  7. Remove the solenoid and nut from the engine.
  8.  

To install:

  1. Installation is the reverse of the removal procedure.
  2.  



Click image to see an enlarged view

Fig. EGR solenoid service-4.5L and 4.9L engines

 
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