There are quite a few things that can cause the engine in your car to run poorly. Most drivers are familiar with failure points such as spark plugs, spark plug wires, fuel pumps, fuel injectors and other items. Not many, however, are familiar with EGR valves, though. In this article, we will look at what EGR valves are and some of the symptoms are when one fails.

What the EGR Valve Does

The EGR valve is a small component that allows the flow of exhaust gases into the intake manifold. As such, it’s a simple valve that closes and opens as needed. Whenever you start the engine in your car, the valve stays in a closed position, blocking the flow of exhaust gases. Once the engine reaches operating temperature, the valve gradually opens, allowing a small amount of burned exhaust gases to enter the intake manifold. If you come to a stop, the valve gradually closes and blocks the flow of exhaust gasses.
After you shut off the engine, the EGR valve closes and remains in that position.

Types of EGR Valves

Gasoline and diesel-powered engines have various EGR system designs. On older vehicle models, you’ll recognize the valve as a round, metal disc about three inches in diameter, usually towards the top of the engine and on one side. These old EGR valves are operated by a vacuum hose.

Later model cars and trucks come equipped with electronic-vacuum EGR valves inside a small block or cylinder. The valve works the same way as in older models, except that it is controlled by the engine’s computer. Just recently, a few manufacturers have implemented a more radical design with EGR jets at the bottom of the intake manifold.

Processing Exhaust Gases

Outside air picked up through the engine’s intake manifold contains close to 80 percent nitrogen and 20 percent oxygen, along with small amounts of other elements. When outside air combines with the fuel and ignites in the combustion chamber, temperatures can reach above 2500 degrees F. Combustion at these temperatures burns the usually inert nitrogen gas, creating oxides of nitrogen (NOx) gases, which cause air pollution. However, when some of the burned exhaust gases are pumped back into the combustion chamber (through the EGR valve), the combustion temperatures decrease and less NOx gases are produced.

Symptoms of a Bad EGR Valve

We contacted our tech consultants at Reedman-Toll Chevy of Exton, a local Chevrolet dealer in Exton, PA and asked them for a quick explanation of what happens when EGR valves go bad. This is what he told us: An EGR valve can basically fail in two ways: It can be jammed open all the time, or it can be closed all the time.

The EGR Valve Sticks Open – This will cause a continuous flow of exhaust gases into the intake manifold. You’ll will probably notice a rough idle upon starting the engine and sometimes when stopped. Gas mileage may decrease also. The Check Engine light on your dashboard may come on too.

The EGR Valve Sticks Closed – This will permanently block the flow of exhaust gases into the intake manifold. You may notice the pinging sound of pre-ignition. Your car will likely fail an emission test. The Check Engine light on your dashboard may come on too.

Troubleshooting

Question: Are the symptoms we discuss above always a sign of EGR problems? Answer: Not always.

There are many other component failures that affect the running of an internal combustion engine and cause the symptoms noted above. For example, an increase in hydrocarbon emissions can be caused by a leaking fuel injector, bad ignition timing, bad compression, bad oxygen sensor, or other problems. An increase in NOx may be caused by a vacuum leak, a clogged fuel injector, low fuel pressure, a leaking head gasket, or other problems. A rough idle may be caused by a faulty ignition coil, a vacuum leak, or an ignition system problem.

Our advice

Clearly troubleshooting and repairing a car or truck with an EGR problem is best done by a certified technician. One of the main reasons for this is that the troubleshooting process involved requires some experience. If you just start replacing items, you may just be wasting money and could cause damage to your engine.


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