The same symptoms that indicate a bad EGR valve can also indicate problems in other parts of the
system. For instance, you can confuse engine performance problems stemming from a bad EGR valve with problems caused by failures in the spark plugs, the spark plug wires, the fuel filter, the fuel pump regulator, and various engine sensors. So, if you don’t do your troubleshooting, you may end up replacing parts unnecessarily and wasting time and money.
To recognize the potential signs of a failing EGR valve, it helps to know a little about an EGR valve: what it does, what it might look like, and how it works inside the combustion chambers or cylinders.
If you're already familiar with the EGR system, jump to the section below on “Symptoms of a Bad EGR Valve.”
Table of Contents
I. What the EGR Valve Does
II. Types of EGR Valves
III. How the EGR Processes Exhaust Gases
IV. Symptoms of a Bad EGR Valve
V. Troubleshooting
I. What the EGR Valve Does
The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it's a simple valve that closes and opens as needed.
The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering.
Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases.
Once the engine reaches operating temperature and speed increases, the valve — either through vacuum or electronic control — gradually opens, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. If you slow down sufficiently or come to a stop, the valve gradually closes and blocks the flow of exhaust gasses. And the process continues for as long as the engine is running.
After you shut off the engine, the EGR valve closes and remains in that position.
II. Types of EGR Valves
Gasoline and diesel-powered engines have various EGR system designs. Vehicles on the road today may use one of six different valve configurations.
On older vehicle models, you'll recognize the valve as a round, thick, metal disc about three inches in diameter, usually towards the top of the engine and on the side.
On these older models, a small-diameter vacuum hose operates a basic EGR valve. The hose connects the top of the valve to the throttle body or carburetor. The valve's metal disk houses a vacuum diaphragm, spring, and plunger.
Later models 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 an electronic EGR position sensor communicates with the car's computer for better control. You may see electric solenoids connected through vacuum lines to the valve as well.
Newer vehicle models use electronic EGR systems that may include additional components, even a digital valve that eliminates the need for vacuum control altogether.
A more radical design, implemented in a few models, was the replacement of the valve with EGR jets at the bottom of the intake manifold.
Some newer high-efficiency engines, for example those with variable valve timing (VVT), don't even use an EGR system.
III. Processing Exhaust Gases
The 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 2500o F (or 1370o C). Combustion at these temperatures burns the usually inert nitrogen gas, creating oxides of nitrogen (NOx) gases, which cause air pollution and human health problems.
However, when the burned exhaust gases are introducted back into the combustion chamber through the EGR valve, extreme temperatures decrease, inhibiting the formation of NOx gases.
IV. Symptoms of a Bad EGR Valve
An EGR valve can fail in two ways: It can be open all the time, or it can be closed all the time.
If the EGR Valve Sticks Open:
This will cause a continuous flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:
A rough idle upon starting the engine (that is, when the engine is cold) and sometimes at a stop light or while looking for a spot in a parking lot (that is, at low engine speeds in a warmed-up engine).
Stalling when the engine idles.
Increase in fuel consumption.
A slight — or strong — fuel odor while operating the vehicle, because of the increase in hydrocarbons leaving the tailpipe (see the next symptom).
Emissions test failure. When the engine is running at low RPM, lower temperatures in the combustion chambers prevent all the fuel from burning, so the flow of unburned hydrocarbon gases coming out of the tailpipe increases significantly.
The Check Engine light (or Malfunction Indicator Light, MIL, depending on your model) illuminates on your dashboard.
If the EGR Valve Sticks Closed:
This will permanently block the flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:
A pinging or tapping noise coming from the engine at low RPM (at speeds higher than idle). The noise is the sound of early ignition of the fuel when it meets high temperatures.
Loud detonations. A second ignition can happen after the normal ignition, and the two can combine with enough power to potentially cause serious engine damage.
Your car fails the emission test. High temperatures in the combustion chamber allow the excessive formation of oxides of nitrogen, which are released through the tailpipe.
The Check Engine light, or Malfunction Indicator Light (MIL), illuminates on your dashboard.
V. Troubleshooting
Are the symptoms above a sign of EGR problems?
Not necessarily.
An increase in hydrocarbon emissions isn’t necessarily caused by a stuck-open EGR valve. Problems in other systems may cause this same symptom as well: a leaking fuel injector, bad ignition timing, bad cylinder compression, bad oxygen sensor, or other problems.
Similarly, 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.
Because these symptoms vary and be caused by different issues, don’t hesitate to troubleshoot the EGR valve and other system components to try to narrow down the problem. This article, How to Test an EGR Valve, gives a series of troubleshooting procedures on vacuum and electrical vacuum-controlled EGR valves, and will help you find out if the problem is your EGR or something else.
Also, because cars with electronic EGR valves will have a Check Engine or MIL light on the dashboard, in these cars you can find out what engine system malfunction triggered the light. With an aftermarket scan tool, you can pull the trouble codes from the computer's memory and see what system or components are causing the problem. Then, you can try to find the fault with the help of the vehicle repair manual for your particular car make and model.
 | |
| EGR valve passages plugged with carbon deposits. |
system. For instance, you can confuse engine performance problems stemming from a bad EGR valve with problems caused by failures in the spark plugs, the spark plug wires, the fuel filter, the fuel pump regulator, and various engine sensors. So, if you don’t do your troubleshooting, you may end up replacing parts unnecessarily and wasting time and money.
To recognize the potential signs of a failing EGR valve, it helps to know a little about an EGR valve: what it does, what it might look like, and how it works inside the combustion chambers or cylinders.
If you're already familiar with the EGR system, jump to the section below on “Symptoms of a Bad EGR Valve.”
Table of Contents
I. What the EGR Valve Does
II. Types of EGR Valves
III. How the EGR Processes Exhaust Gases
IV. Symptoms of a Bad EGR Valve
V. Troubleshooting
I. What the EGR Valve Does
The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it's a simple valve that closes and opens as needed.
The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering.
Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases.
Once the engine reaches operating temperature and speed increases, the valve — either through vacuum or electronic control — gradually opens, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. If you slow down sufficiently or come to a stop, the valve gradually closes and blocks the flow of exhaust gasses. And the process continues for as long as the engine is running.
After you shut off the engine, the EGR valve closes and remains in that position.
II. Types of EGR Valves
Gasoline and diesel-powered engines have various EGR system designs. Vehicles on the road today may use one of six different valve configurations.
On older vehicle models, you'll recognize the valve as a round, thick, metal disc about three inches in diameter, usually towards the top of the engine and on the side.
On these older models, a small-diameter vacuum hose operates a basic EGR valve. The hose connects the top of the valve to the throttle body or carburetor. The valve's metal disk houses a vacuum diaphragm, spring, and plunger.
Later models 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 an electronic EGR position sensor communicates with the car's computer for better control. You may see electric solenoids connected through vacuum lines to the valve as well.
Newer vehicle models use electronic EGR systems that may include additional components, even a digital valve that eliminates the need for vacuum control altogether.
A more radical design, implemented in a few models, was the replacement of the valve with EGR jets at the bottom of the intake manifold.
Some newer high-efficiency engines, for example those with variable valve timing (VVT), don't even use an EGR system.
III. Processing Exhaust Gases
The 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 2500o F (or 1370o C). Combustion at these temperatures burns the usually inert nitrogen gas, creating oxides of nitrogen (NOx) gases, which cause air pollution and human health problems.
However, when the burned exhaust gases are introducted back into the combustion chamber through the EGR valve, extreme temperatures decrease, inhibiting the formation of NOx gases.
IV. Symptoms of a Bad EGR Valve
An EGR valve can fail in two ways: It can be open all the time, or it can be closed all the time.
If the EGR Valve Sticks Open:
This will cause a continuous flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:
A rough idle upon starting the engine (that is, when the engine is cold) and sometimes at a stop light or while looking for a spot in a parking lot (that is, at low engine speeds in a warmed-up engine).
Stalling when the engine idles.
Increase in fuel consumption.
A slight — or strong — fuel odor while operating the vehicle, because of the increase in hydrocarbons leaving the tailpipe (see the next symptom).
Emissions test failure. When the engine is running at low RPM, lower temperatures in the combustion chambers prevent all the fuel from burning, so the flow of unburned hydrocarbon gases coming out of the tailpipe increases significantly.
The Check Engine light (or Malfunction Indicator Light, MIL, depending on your model) illuminates on your dashboard.
If the EGR Valve Sticks Closed:
This will permanently block the flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:
A pinging or tapping noise coming from the engine at low RPM (at speeds higher than idle). The noise is the sound of early ignition of the fuel when it meets high temperatures.
Loud detonations. A second ignition can happen after the normal ignition, and the two can combine with enough power to potentially cause serious engine damage.
Your car fails the emission test. High temperatures in the combustion chamber allow the excessive formation of oxides of nitrogen, which are released through the tailpipe.
The Check Engine light, or Malfunction Indicator Light (MIL), illuminates on your dashboard.
V. Troubleshooting
Are the symptoms above a sign of EGR problems?
Not necessarily.
An increase in hydrocarbon emissions isn’t necessarily caused by a stuck-open EGR valve. Problems in other systems may cause this same symptom as well: a leaking fuel injector, bad ignition timing, bad cylinder compression, bad oxygen sensor, or other problems.
Similarly, 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.
Because these symptoms vary and be caused by different issues, don’t hesitate to troubleshoot the EGR valve and other system components to try to narrow down the problem. This article, How to Test an EGR Valve, gives a series of troubleshooting procedures on vacuum and electrical vacuum-controlled EGR valves, and will help you find out if the problem is your EGR or something else.
Also, because cars with electronic EGR valves will have a Check Engine or MIL light on the dashboard, in these cars you can find out what engine system malfunction triggered the light. With an aftermarket scan tool, you can pull the trouble codes from the computer's memory and see what system or components are causing the problem. Then, you can try to find the fault with the help of the vehicle repair manual for your particular car make and model.
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