In modern gasoline and diesel engines, EGR valves are used for precise control of the combustion of the mixture, in order to increase economy and reduce the amount of nitrogen oxides and carbon.
The EGR valve serves to introduce a smaller or larger amount of exhaust gas into the mixture of fresh air and fuel, which regulates combustion. Things are very simple. Too much oxygen creates a warm flame and quick combustion of the mixture.
As a reaction to the increase in temperature in the combustion chamber, an unwanted chemical reaction occurs between oxygen and nitrogen from the intake air, which in turn creates toxic nitrogen oxides. As a consequence, in addition to the increased environmental pollution, due to the iteration with nitrogen, the engine mixture itself is left with less oxygen to burn the fuel , thereby reducing power, increasing the level of carbon-hydrogen. When you add an adequate amount of oxygen-free exhaust gas to the superheated mixture, the combustion temperature is lowered and the engine operating parameters returned to normal.
For gasoline engines, EGR reduces the possibility of self-ignition. As a direct consequence, it is possible to use a higher compression ratio and a different ignition time to obtain a more resilient engine. For diesel engineers, there is a noticeable reduction in detonation noise when operating on the back.
The EGR valve does the opposite for gasoline and diesel.
With diesel, it is fully open when operating at a minimum and can provide up to 50 percent of the presence of combustion gases in the combustion chamber. When increasing power and revs, it closes completely. For a change, the gasoline EGR is completely closed on the back and slowly opens with increasing power. Yet, the maximum share of exhaust in gasoline is only five to ten percent.
The EGR valve is subject to failure due to clogging, primarily due to the deposition of soot particles. The valve may remain fully open, fully closed, or may have a slow reaction. If the header is in the open position, gasoline will cause poor performance and gasoline will cause a reduction in power and black smoke from the exhaust.
If the EGR remains closed, it will cause excessive thrashing for the diesel engine and increased fuel consumption for the gasoline.
What to do?
When the EGR valve fails, the only real repair is replacement. It is recommend that you always use a high quality replacement part that fully meets the factory specifications. Recommendation is to thoroughly check and clean the connection hoses and connectors when replacing the valves.