An EGR valve is an Exhaust Gas Recirculation valve. An EGR valve is a valve that allows a portion of your motor’s hot combusted gas to re-enter the intake manifold to be mixed in with the incoming air into the motor to be recombusted in order to further reduce the emissions output of the vehicle and lower internal combustion temps. The way this works is that during initial combustion a portion of the exhaust gas emanating is composed of hazardous environmental gaseous products such as Nitric Oxides NO2’s, Carbon Monoxide, Carbon Dioxide etc. By reintroducing a portion of this gas back into the combustion chamber to be combusted a second time, the motor will actually run cooler due to introduction of more inert gasses such as NOx into the system which keeps the cylinders under 2500 degree F. So the net result with a properly working EGR valve in your system is a lowered internal combustion chamber temperature which actually means lowered harmful emissions (the motor produces more harmful NOx gases if its internal temps are above 2500 deg F).
An EGR valve works via a valve that opens and closes to allow more or less combusted exhaust gas back into your intake manifold. This gas comes from your exhaust manifold to mix in with the incoming air back into your intake. The EGR valve is either actuated via pressure from your exhaust manifold i.e. opens when enough pressure is pushing on the plate and spring. Or in newer generation vehicles it is computer controlled via electronics which allow the valve to open and close according to computer feedback. This is why it is very important to make sure the EGR valve is clean and free from carbon deposits and working properly. A non functioning or clogged EGR can lower gas mileage, raise under hood temperatures and cause you to lose horsepower as well.
Generally on vehicles with over 100,000 miles on them the EGR may either have a clogged or hard to actuate valve that is filled with carbon deposits from years of hot carbon sooty exhaust gas contacting the valve. Sometimes the EGR valve will throw an engine code if it is really bad. However many times it will not but still needs to be de-carboned and cleaned to restore proper performance and improve gas mileage. In addition over time and much mileage the actual EGR gasket may leak much like a valve cover or intake manifold gasket can leak causing vacuum issues in the motor. So sometimes by changing the EGR valve gasket you may be closing a vacuum leak that you didn’t know you had.
There are a few fixes for a faulty or carbon filled EGR valve, the cheaper fix and the more expensive fix.
1. If you are looking to save money and your motor is not throwing an EGR code, a simple clean and fresh gasket install will restore like new performance to your once faulty EGR valve. In order to do this you must remove the EGR valve according to the proper instructions from your repair manual. Once you have removed the EGR valve remove the built up carbon in the valve using a carburetor cleaner product Any brand such as Gunk, CRC, or Autozone will do.
Before you do this take a scraper and emory cloth and remove the old gasket that is caked onto the bottom of the EGR valve. This process may take a while so be patient. Once all of the old gasket is removed clean the carbon out of the EGR chamber by spraying your carb cleaner into the port hole on the bottom of the EGR valve. You will have to do this many times in order to clean out all of the carbon. Also remember to spray the other port which will be shut with the valve stop on the bottom. You should be able to see the black carbon around the circumference of the stopper valve. After removing all the carbon from the valve you must let it dry thoroughly before installing back on the motor with a fresh gasket you can pick up at your local auto parts store. Install your clean EGR valve with a new gasket to the proper torque specs listed in your repair manual. If your valve was partially or totally stuck due to carbon buildup then you may notice a power increase and an increase in your fuel economy.
2. If you are not mechanically inclined or the cleaning trick does not fix the EGR code then consider replacing the whole EGR valve. You can purchase a new EGR valve at your local parts store. Either way you will have a new or like new flowing condition in your EGR valve which should go a long way at improving your mpg’s.