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June-19-09

An Introduction To Your Car’s Exhaust Gas Recirculation

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An Introduction To Your Car’s Exhaust Gas Recirculation

While you’re driving, your vehicle’s engine creates a number of emissions. Some, like hydrocarbons, are regulated in many jurisdictions by smog checks. Others, like nitrogen oxide (or, NOx), are not. Even though NOx is unregulated, it does add to pollution. In order to reduce the amount that is produced, your car is equipped with an exhaust gas recirculation – or EGR – system.

Most motorists have likely heard of this assembly, but don’t know much about it. I’ll briefly describe how it works and explain problems that can occur if it fails (a failure leads to more than just increased emissions). I’ll also provide an overview of the part that helps control the flow of exhaust.

How It Works

As mentioned, your car produces emissions through the exhaust. The intake manifold sends fuel and air to the cylinders where combustion happens. Without the EGR system, the temperatures that are generated during combustion would rise to a point in which oxygen and nitrogen react with each other. When that happens, nitrogen oxide is produced.

Your vehicle’s exhaust gas recirculation assembly prevents those combustion temperatures from rising that high. It does so by leaking a small amount of gas (less than 10%) from the exhaust back into the intake manifold. When it enters, it cools the area surrounding the combustion of the air and fuel mixture. As a result, it reduces the interaction between the oxygen and nitrogen.

Overview Of Different Valves

EGR valves are used to control the amount of gas that is recirculated into the intake manifold. Depending upon the age of your car, this part may be electronic or regulated by vacuum. When your vehicle idles, the valve closes and thereby, prevents the leaking described above. When your engine heats up through combustion, the valve opens.

There are 6 main types of valves, though a couple of them are only found in older cars. They include ported, positive and negative backpressure, pulse-width, digital, and linear electronic valves. Each of them works in a slightly different manner, yet perform the same basic function for your vehicle’s EGR system.

Problems That Can Occur

You might think that since the EGR controls the level of nitrogen oxide in your vehicle’s emissions, there is little harm in the assembly malfunctioning or failing. After all, NOx levels are unregulated. In reality, a malfunctioning exhaust gas recirculation system can cause your engine to start pinging. Also, if the EGR valve fails to close properly, too much leaking into the intake manifold can occur. That can lead to misfiring, poor idling, or a hard starting problem.

Unless you have experience repairing problems under the hood, you should have a trained auto technician fix a failing EGR assembly. He’ll be able to run a diagnostic check, troubleshoot the issue, and replace any malfunctioning parts, if necessary. What’s more, he’ll do it correctly the first time.