What Is EGR?
Exhaust gas recirculation (EGR) is a system that takes exhaust gas from a diesel’s exhaust manifold and reintroduces it into the intake of the engine to reduce the combustion chamber temperature.
Why do modern diesels have EGR? you ask. Basically, EGR is used to reduce the formation of NOx emissions, which are created when the combustion chamber temperature exceeds 2,370 degrees. Pumping exhaust (EGR) back into the engine helps to cool the combustion chamber because EGR has almost no oxygen in it. Without oxygen, the temperature stays below the NOx-producing threshold, and the emissions coming out the tailpipe are cleaner.
Unfortunately, the EGR gasses from a diesel tend to bring a sooty mess with themit’s a lot like cholesterol in your body. That sooty mess tends to gum up the EGR valve, EGR cooler, intake ports, and any sensors that are exposed to it.