In automobiles the exhaust gas recirculation (EGR) valve is a device for diverting exhaust gases into the intake manifold. As the name implies, the EGR valve circulates a regulated amount of exhaust into the intake manifold, lowering the temperature of the air-fuel mixtures and reducing pollutants. The EGR valve is a vital part of the emissions system and plays an important role in the overall operation of the engine.
Types
On older cars the EGR valve is mechanically operated, and on newer vehicles is typically electronic in operation. Both types serve the same purpose and differ only in how their operation is controlled. Mechanical versions usually utilize vacuum from the engine to actuate the valve, while electronic versions may make use of both vacuum and computer signals to activate the valve. A smaller number of new cars rely entirely on electronics to control the EGR valve.
Location
The EGR valve is usually located on the intake manifold near or over the rear of the engine. In some cases, it is located on the side of the engine and mounted on a tube connected to the exhaust pipe. It is typically saucer shaped and, if mechanical, will have one or more small hoses connected to it, while the electronic versions will have only one or none.
Operation
Whether it is electronically or mechanically operated, the EGR valve introduces a regulated amount of exhaust gas into the fuel and air mixture, which is then burned by the engine in the combustion chambers. Contrary to conventional wisdom, the introduction of exhaust gases into the fuel-air mixture actually has a cooling effect, which improves overall combustion, resulting in more complete burning of fuel. In this way the EGR valve assists in lowering levels of noxious gases within the exhaust.
Problems
A faulty EGR valve can cause several trouble symptoms to appear. These directly relate to the operation of the engine and emission systems with no effect on the automatic overdrive (AOD) transmission, driveline or nonemission-related equipment. Symptoms can include stalling, rough idle, hesitation upon acceleration and overall power reduction.
Solutions
Generally the EGR valve is not a readily serviceable part. It is usually a sealed component with little access available to internal workings. Occasionally carbon from the exhaust system can build up inside the valve's intake orifice, causing the valve to stick, hampering its ability to open and close. In these cases, cleaning can often solve the problem. Apart from cleaning, a faulty EGR valve usually needs complete replacement to restore correct operation of the engine.