EGR Valves & Components

The EGR (Exhaust Gas Recirculation) valve meters exhaust gas into the intake air stream to lower combustion chamber temperature and reduce NOx (oxides of nitrogen) emissions. NOx reacts with VOCs (Volatile Organic Compounds) in the presence of sunlight to form harmful smog. NOx forms when nitrogen combines with oxygen at extremely high combustion chamber temperatures, 2500°F (1371°C) or more. Diluting the incoming air/fuel mixture with exhaust gas lowers combustion temperature, reducing the amount of nitrogen molecules that bond with oxygen molecules, thereby diminishing the formation of NOx. However, exhaust gas recirculation must only occur during certain engine operating conditions, and if there’s a malfunction, it could result in excessive NOx emissions, rough idle, stalling, detonation, or other drivability problems. If you’re experiencing defective EGR symptoms, we have the EGR valves and related components to restore proper vehicle performance and emissions compliance.

It may sound counterintuitive to apply a hot gas to lower temperature, but exhaust is used because it’s a readily available inert gas. All oxygen is consumed during combustion, so exhaust gas will not burn. The exhaust gas occupies space in the combustion chamber that would otherwise be taken up by the air/fuel mixture. Air is comprised of 21% oxygen, so the exhaust gas reduces the amount of oxygen in the combustion chamber that would be available for combustion and raise the temperature. Substituting the inert exhaust gas for the oxygen reduces combustion temperature. In addition to lowering NOx emissions, EGR can also prevent engine damaging detonation, commonly called engine knock, which can also be caused by elevated combustion chamber temperature.

The EGR valve is mounted in a passage that connects the exhaust system to the intake manifold. When it opens it allows exhaust to mix with the incoming air charge to the combustion chambers. The valve is necessary because EGR must be controlled. Diluting the intake air charge with exhaust is only desirable when the vehicle is at cruising speed or during light acceleration. When the engine is cold, EGR isn’t needed because combustion temperatures aren’t hot enough to form NOx and adding exhaust would cause the engine to run rough and stall. The same is true at idle speed even when the engine is warmed up and at operating temperature. And with the richer air/fuel mixture that occurs at WOT (Wide Open Throttle) and during hard acceleration, EGR is also unnecessary.

The valve inside the EGR valve that regulates exhaust flow is either controlled by a vacuum operated diaphragm or an electric motor within the EGR valve assembly. Before the advent of computerized engine control systems, a thermal vacuum switch was used to prevent EGR when the engine was cold. Today EGR function is computer controlled. In addition to ported vacuum EGR valves, other designs that have been used include positive backpressure EGR valves and negative backpressure EGR valves, which both vary valve opening according to exhaust backpressure; pulse-width modulated electronic EGR valves that are used with an EGR vacuum control solenoid; and electronic digital and linear EGR valves.

Additional components specific to the type of EGR system and EGR valve have been used in combination with the various EGR valves, such as sensors to provide feedback to the computer on EGR flow, and solenoids to regulate the vacuum signal to the EGR valve. These include vacuum switches, solenoids, and modulators, and pressure, temperature and valve position sensors. Some systems include EGR coolers to lower the temperature of the exhaust before it mixes with the air charge to further assist with combustion chamber cooling. The complexity and variation of components and systems precludes a detailed description of the function of each component and operation of every system within the confines of this product description. When working properly, the EGR valve and related components ensure EGR only when it’s optimal for NOx reduction without adversely affecting engine performance. Too much EGR or EGR at the wrong time is indicated by rough idle, stalling, hesitation, and poor acceleration. Symptoms of insufficient EGR include spark knock and a failed inspection due to excessive NOx emissions.

In addition to component failure, EGR problems can also be caused by carbon buildup that causes the valve to stick and/or block EGR passages. If incorrect EGR flow is detected by sensors, one or more DTCs (Diagnostic Trouble Codes) will be set in the computer’s memory and the CHECK ENGINE light will turn on. Vacuum operated valves can be tested with a vacuum pump, but a scan tool is generally required to test fully electronic EGR valves and for more comprehensive testing. No matter what vehicle you’re working on or the type of EGR system, we have the replacement EGR valves and related components to restore proper performance and emissions compliance. We offer components that are manufactured to original equipment specifications, so when repairs are completed you can count on the performance your vehicle was designed to deliver. In addition to the components described above, we also offer parts that are often needed to achieve a complete repair including tubes, lines, fittings, hoses, connectors, gaskets, and much more.