GM: Electra/Park Avenue/Ninety-Eight 1990-1993

Exhaust Gas Recirculation System

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Fig. Fig. 1 Digital egr valve components



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Fig. Fig. 2 egr valve location-Vin C engine

OPERATION



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 combustion chamber. 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. The 3.8L (vin L) engine only does not use an egr valve.

The egr valve controls egr flow from the exhaust to the intake manifold. With this Digital version, the egr valve is purely electrical and uses solenoid valves to open the flow passage. 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.

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

The Digital egr valve is designed to control the flow of egr independent of intake manifold vacuum. The valve controls egr flow through 2 (vin 1) or 3 (vin C) solenoid-opened orifices, which increases in size, to produce 4 (vin 1) or 7 (vin C) possible combinations. When a solenoid is energized, the armature with attached shaft and swivel pintle, is lifted, opening the orifice.

The Digital egr valve is opened by the ecm, grounding each solenoid circuit individually. The flow of egr is regulated by the ecm which uses information from the Coolant Temperature Sensor (cts), Throttle Position Sensor (tps) and Manifold Absolute Pressure (map) sensor to determine the appropriate rate of flow for a particular engine operating condition.

TESTING



To be accurately diagnosed, this system must be checked using a Tech 1 Scan tool, or similar device.

REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable.
  2.  
  3. Remove the decorative cover from the top of the valve.
  4.  
  5. Disconnect the electrical connector at the solenoid.
  6.  
  7. Remove the 2 base-to-flange bolts.
  8.  
  9. Remove the digital egr valve and discard the gasket.
  10.  

To install:

  1. Clean the mating surfaces of the egr valve and its mounting surface.
  2.  
  3. Install a new gasket and the digital egr valve.
  4.  
  5. Install the 2 base-to-flange bolts. Tighten to 22 ft. lbs. (30 Nm).
  6.  
  7. Connect the electrical connector and install the decorative cover.
  8.  
  9. Connect the negative battery cable and check the system for proper operation.
  10.  

 
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