Buick 1997578 SOL,EGR/EF

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The 2-barrel engines have EGA with a metering valve, vacuum line to the carburetor, and exhaust gas passages cast into the intake manifold. Called the EGA valve, this one is operated by the vacuum from the carburetor and opens and closes to enable the mixture of the exhaust gases with the fuel and air to provide a non-misfire or pinging at part throttle. This system reduces combustion temperature and hence decrease nitrogen oxides (NOx) emission, with the valve closed at idle and at full throttle. In many configurations, it is a thermal vacuum switch that regulates vacuum to the EGR valve in order to eliminate stalling and rough idle when the engine is cold. As the vehicle accelerates, the valve opens at specific vacuum with direct aim of admitting exhaust gases into the mixture. Some of the California engines have a provision that includes a dual diaphragm EGR valve to help in operation during non-constant vacuum conditions. Starting from models of the year 1977, manufacturers have employed back pressure EGR valves which are triggered by exhaust back pressure in order to control the EGR flow with respect to the load on the engine. The later models incorporate ported signal vacuum EGR valves and the particular systems employ pulse width modulation in order to control EGR under some circumstances. Measures that are taken to test for EGA issues include checking for EGA that is either too large or small, examining the vacuum hoses and testing the functionality of the EGA valve. An EGR valve and the thermal vacuum switch are removed and reinstalled in the system; details should be paid to vacuum lines, and sealing should be appropriate.

Maintenance primarily involves inspecting vacuum hoses and the EGR valve, with the thermal vacuum switch being the only moving part that may wear out.

If the diaphragm does not move or moves only with much effort, it is recommended to replace the EGR valve with a new one.