Dodge Colt/Challenger/Conquest/Vista 1971-1989 Repair Guide

Exhaust Gas Recirculation System

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OPERATION





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Fig. Fig. 1 Common EGR system air flow routing



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Fig. Fig. 2 Cutaway view of the EGR valve

The EGR system recirculates part of the exhaust gases into the combustion chambers. This dilutes the air/fuel mixture, reducing formation of oxides of nitrogen in the exhaust gases by lowering the peak combustion temperatures.

The parts of a typical EGR system are:


EGR valve-Operated by vacuum drawn from a point above the carburetor throttle plate. The vacuum controls the raising and lowering of the valve pintle to allow exhaust gases to pass from the exhaust system to the intake manifold.
 
Thermo Valve-Used to stop EGR valve operation below approximately 131°F (55°C), in order improve cold driveability and starting.
 
Dual EGR Valve-(1978 and Later) The EGR vacuum flow is suspended during idle and wide open throttle operation. The primary valve controls EGR flow when the throttle valve opening is relatively narrow, while the secondary control valve operates at wider openings.
 
Sub-EGR Control Valve-Linked to the throttle valve to closely modulate the EGR gas flow.
 

MAINTENANCE





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Fig. Fig. 3 Some EGR valves may be tested using a vacuum pump by watching for diaphragm movement



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Fig. Fig. 4 A manifold vacuum gauge can be used to check a variety of vacuum-controlled components

  1. Check all vacuum hoses for cracks, breakage and correct installation.
  2.  
  3. Check EGR valve operation by applying vacuum to the EGR valve vacuum nipple with the engine idling. The idle should become rough.
  4.  
  5. Check the passages in the cylinder head and intake manifold for clogging. Clean as necessary.
  6.  
  7. Cold start the engine. The EGR port nipple should be open. When the coolant is warmed to over 131°F (55°C), the port should be closed.
  8.  

REMOVAL & INSTALLATION



EGR Valve
  1. Remove the vacuum hose.
  2.  
  3. Disconnect the exhaust line from the EGR valve.
  4.  
  5. Remove the EGR valve.
  6.  
  7. Install the EGR valve. Be sure to tighten the nut on the EGR line to 22-25 ft. lbs.
  8.  

Thermo Valve


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Fig. Fig. 5 Cutaway view of the thermo valve

The thermo valve is located on the left side of the intake manifold. It is threaded into the manifold and can be removed with an openend wrench.

  1. Disconnect the vacuum lines.
  2.  
  3. Using an open-end wrench, carefully turn the thermo valve out of the intake manifold.
  4.  
  5. Apply a good sealer to the valve threads before installation.
  6.  
  7. Connect the vacuum lines. The A nipple should be connected to the vacuum hose from the carburetor and the B nipple to the EGR valve.
  8.  

 
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