Chevrolet Nova/ChevyII 1962-1979

Exhaust Gas Recirculation System

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OPERATION





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Fig. Fig. 1 Exhaust Gas Recirculation (EGR) system schematic-1966-74 vehicles shown



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Fig. Fig. 2 Cross-sectional view of a single diaphragm EGR valve



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Fig. Fig. 3 Cross-sectional view of a dual diaphragm EGR valve

All 1973 and later engines are equipped with Exhaust Gas Recirculation (EGR). This system consists of a metering valve, a vacuum line to the carburetor, and internal exhaust gas passages in the intake manifold. The EGR valve is controlled by carburetor vacuum, and accordingly opens and closes to admit exhaust gases into the fuel/air mixture. The exhaust gases lower the combustion temperature and reduce the amount of oxides of nitrogen (NO x ) produced. The valve is closed at idle and wide open throttle, but is open between the two extreme throttle positions.

Some California engines are equipped with a dual diaphragm EGR valve. This valve further limits the exhaust gas opening (compared to the single diaphragm EGR valve) during high intake manifold vacuum periods, such as high-speed cruising, and provides more exhaust gas recirculation during acceleration when manifold vacuum is low. In addition to the hose running to the thermal vacuum switch, a second hose is connected directly to the intake manifold.

REMOVAL & INSTALLATION



EGR Valve


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Fig. Fig. 4 EGR valve mounting on a 6-cylinder engine



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Fig. Fig. 5 Unfasten the EGR valve retaining bolts ...



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Fig. Fig. 6 ... then remove the EGR valve. Note that on in-line 6-cylinder engines, the EGR valve is mounted to the carburetor

  1. Pull the vacuum sensing line from the fitting on top of the EGR valve.
  2.  
  3. Unfasten the bolt which secures the valve clamp to the manifold, or carburetor, as applicable.
  4.  
  5. Remove the clamp and the EGR valve from the manifold, or carburetor, as applicable.
  6.  
  7. Installation is the reverse of removal. Use a new valve gasket. Tighten the clamp bolt to 25 ft. lbs. and lock it with its tab, if equipped.
  8.  

 
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