The Exhaust Gas Recirculation Valve or (EGR) Valve as most refer to it is designed to cool exhaust gas by burning exhaust for a second time within the intake system.
This result is the reduction of nitrogen oxide emissions. Recirculation of the exhaust leads to a gradual accumulation of carbon particles inside the inlet. To recirculate exhaust back into the intake manifold, a small calibrated “leak” or passageway is created between the intake and exhaust manifolds.
Intake vacuum in the intake manifold sucks exhaust back into the engine. The amount of recirculation has to be closely controlled otherwise it can have an adverse effect on idle quality, engine performance and drive ability as a huge vacuum leak.
Soot forms where the exhaust passes into the intake, and even within the valve itself, causing various problems. Fuel injectors, which are delicate and expensive components of the engine, may become partially clogged. As for the EGR valve, soot and grime may prevent it from properly opening and closing. If it becomes stuck in the closed position, it will lose all function.
The vehicle will continue to run properly, however it will emit nitrogen oxides at levels beyond the threshold of what is legally tolerated according to area regulations. On the other hand, if the EGR valve becomes stuck in an open position, the engine will become saturated at an even faster rate. Over time, the vehicle will lose acceleration power and certain symptoms will manifest, such as persistent stalling.
COMMON EGR PROBLEMS
- Pinging (spark knock or detonation) because the EGR system is not working, the exhaust port is plugged up with carbon, or the EGR valve has been disabled.
- Rough idle or misfiring because the EGR valve is not closing and is leaking exhaust into the intake manifold. You may also find a P0300 random misfire code on OBD II vehicles.
- Hard starting because the EGR valve is not closing and is creating a vacuum leak into the intake manifold.
An EGR valve that is stuck open:
When the EGR is stuck open, it will lead to a vacuum leak which in turn causes inefficient combustion, hesitation, rough idling and even stalling. The reason for this is that the car cannot combust on the carbon dioxide emitted from the tailpipe. An open EGR valve causes exhaust emissions to flood the combustion chamber, hence preventing it from functioning as it should. To check for a stuck open EGR valve, idle a parked car with the brake on and have someone examine the plunger shaft to see if it is stick open.
An EGR valve that is stuck closed:
This causes nitrogen oxide emissions to rise and the car might start to knock. A sharp knock occurs when the fuel in the combustion chamber ignites before the explosion in the cylinder reaches it. This leads to a disruption in engine timing. When this happens, warm up your engine and rev it, then check if the EGR valve will move.
EGR valves have changed design many times over the years.
Most older EGR systems use a vacuum regulated EGR valve while newer vehicles tend to have an electronic EGR valve to control exhaust gas recirculation. At idel speed the EGR valve should look closed. There is no EGR flow into the manifold. The EGR valve remains closed until the engine is warm and is operating under load. As the load increases and combustion temperatures start to rise, the EGR valve opens and starts to leak exhaust back into the intake manifold. This has a quenching effect that lowers combustion temperatures and reduces the formation of NOx.
Here are some of the changes:
- Ported EGR valves (1973 to 1980s).
- Positive backpressure EGR valves (1973 & up).
- Negative backpressure EGR valves (1973 & up).
- Pulse-width modulated electronic EGR valves (early 1980s & up).
- Digital electronic EGR valves (late 1980s to 1990s).
- Linear electronic EGR valves (early 1990s & up).
NOT ALL ENGINES HAVE A EGR VALVE
On many late model engines with Variable Valve Timing-(VVT), there is NO EGR valve because the VVT system varies the timing of the exhaust valves to provide the same effect as EGR. By changing the point at which the exhaust valves close when the engine is working hard under load, a small amount of exhaust gas can be retained in the cylinders for the next combustion cycle. This has the same effect on reducing combustion temperatures and NOx as recirculating exhaust gas from an exhaust port back into the intake manifold through an EGR valve. The big difference is that the VVT system can react to changing engine loads much more quickly and precisely than a traditional EGR valve. Using VVT for EGR also eliminates many of the problems associated with EGR valves such as carbon buildup and valve sticking or failure.
Find out what kind of EGR valve is on the vehicle so you can use the appropriate test procedure. Examine the valve or refer to a service manual. On some vehicles, you may find this information on the underhood emissions decal. Also, find out what kind of vacuum controls are used in the vacuum plumbing. Does it have a ported vacuum switch or a solenoid? Follow the vacuum connections from the valve, refer to a service manual or the underhood emissions decal for vacuum hose routing information.
There are several ways to troubleshoot an EGR system. You can follow the EGR troubleshooting procedure that’s listed in a service manual for the engine. On late model computer controlled engines, there may be trouble codes that relate to the EGR system. On such an application, the first step would be to read out the code or codes using a scan tool or code reader. You would then refer to the specific diagnostic charts in a service manual that tell you what to do next.
EGR Trouble Codes:
On pre-OBD II GM applications, a code 32 indicates an EGR problem. The logic by which the onboard diagnostics detects trouble follows one of two routes. On some applications, a code 32 is set when the computer detects a richer fuel mixture off idle (indicating no EGR). On others, a code is set if the computer energizes the EGR vacuum solenoid but does not detect a corresponding drop in intake vacuum.
EGR TROUBLESHOOTING PROCEDURE
1. Does the engine have a detonation (spark knock) problem when accelerating under load? Refer to the timing specs for the engine and check ignition timing. You may find the timing could be over advanced. If the timing is within specs, check the engine’s operating temperature. A cooling problem may be causing the engine to detonate. If the temperature is within its normal range and there are no apparent cooling problems, other possibilities to investigate include spark plugs that are too hot for the engine application, a lean air/fuel mixture, low octane fuel or too much compression (due to a buildup of carbon in the combustion chambers or because of pistons or heads that have too much compression for the fuel you’re using). Be sure you have ruled out all the other possibilities before focusing on the EGR system.
2. Use a vacuum gauge to check the EGR valve vacuum supply hose for vacuum at 2000-2500 rpm. There should be vacuum if the engine is at normal operating temperature. No vacuum would indicate a problem such as a loose or misrouted hose, a blocked or inoperative ported vacuum switch or solenoid, or a faulty vacuum amplifier (or vacuum pump in the case of a diesel engine).
Sometimes loss of EGR can be caused by a failed vacuum solenoid in the EGR‘s vacuum supply line. Refer to a vacuum hose routing diagram in a service manual or the hose routing information on the vehicle’s emission decal for the location of the solenoid. If the solenoid fails to open when energized, jams shut or open, or fails to function because of a corroded electrical connection, loose wire, bad ground, or other electrical problem, it will obviously affect the operation of the EGR valve.
Depending on the nature of the problem, the engine may have no EGR, EGR all the time, or insufficient EGR. If bypassing the suspicious solenoid with a section of vacuum tubing causes the EGR valve to operate, find out why the solenoid isn’t responding before you replace it. The problem may be nothing more than a loose or corroded wiring connector.
3. Inspect the EGR valve itself. Because of the valve’s location, it may be difficult to see whether or not the valve stem moves when the engine speed is increased to 1500 to 2000 rpm by slowing opening and closing the throttle. The EGR valve stem should move if the valve is functioning correctly. A hand mirror may make it easier to watch the valve stem. Be careful not to touch the valve because it will be hot! If the valve stem doesn’t move when the engine speed is increased, there’s probably something wrong with the EGR valve.
Another way to “test” the EGR valve on some engines is to apply vacuum directly to the EGR valve. Note; This only works on ported vacuum EGR valves, not back pressure EGR valves or electronic EGR valves. Vacuum should pull the valve open creating the equivalent of a large vacuum leak. This should cause a momentary drop in idle speed and a noticeable increase in idle roughness.
Back pressure type EGR valves are more difficult to check. There must be sufficient back pressure in the exhaust before the valve will open when vacuum is applied. One trick that’s sometimes used is to create an artificial restriction by inserting a large socket into the tailpipe, then applying vacuum to the valve to see if it opens. Don’t forget to remove the restriction afterwards.
4. Remove and inspect the EGR valve if you suspect a problem. Most failures are caused by a rupture or leak in the valve diaphragm. If the valve is not a back pressure type, it should hold vacuum when vacuum is applied with a hand-help pump. If it can’t hold vacuum, it needs to be replaced. Note: This test does not work on back pressure EGR valves.
Back pressure EGR valves sometimes fail if the hollow valve stem becomes clogged with carbon or debris. This you can see for yourself. It’s almost impossible to remove such a clog, so replace the EGR valve.
Carbon accumulation around the base of the EGR valve can sometimes interfere with the opening or closing of the valve. Do not soak the entire valve in solvent or allow solvent to get anywhere near the diaphragm. The solvent will attack and ruin the diaphragm.
5. Inspect the EGR passageway in the manifold for clogging. Use a pipe cleaner or small piece of wire to explore the opening for a blockage. Sometimes you can dislodge material that’s clogging the opening by carefully poking at it. Other times, it may be necessary to remove the manifold and have it professionally cleaned. Also recommended is to clean the throttle body and intake manifold at the same time to remove varnish and carbon deposits.
HOW TO CLEAN YOUR EGR VALVE
If your car is running poorly, it might be a sign that your EGR valve has a problem. Here’s how to go about EGR valve cleaning that you can do it by yourself.
- Remove the vacuum line connected to the EGR valve. If the vacuum line looks, brittle, frayed or broken, replace it.
- If the EGR valve has an electrical connection, disconnect the harness carefully.
- Unbolt the EGR valve from the engine. Give it a slight tap if it doesn’t come right off. You can use a tiny hammer or a block of wood to do this.
- Remove your gasket if it looks frayed, torn or disintegrated. You can reuse it if it’s in good condition.
- Soak your EGR valve in a bowl of carb cleaner. Avoid submerging the electrical portion if it has one. You should soak it overnight if possible.
- After soaking the valve in the cleaner, you should clean the openings, passages and surfaces by using a small brush. You can also use a toothbrush or a pipe cleaner for this. Make sure to have eye protection and chemical resistant gloves because the carb cleaner is harsh.
- The final step is to reinstall the EGR valve. Remember to reattach the vacuum hose and electrical connections if you had any.
Soon we will see all the new challenges with NO EGR in all the late model engines with Variable Valve Timing-(VVT)
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