The (EGR) valve, is designed to cool exhaust gas; by burning exhaust for a second time, within the intake system.
Consequently, this results in the reduction of, nitrogen oxide emissions.
But, recirculation of the exhaust, leads to a gradual accumulation of, carbon particles inside the inlet.
The (EGR) valve, is used to recirculate exhaust, back into the intake manifold. Therefore, a small calibrated “leak” or passageway is created between the, intake and exhaust manifolds.
So, intake vacuum in the intake manifold, sucks exhaust back into the engine. But, the amount of recirculation has to be controlled; otherwise it can have an adverse effect as a, huge vacuum leak. Furthermore, soot forms where the exhaust passes into the intake and even within the valve itself, causing various problems. Consequently, fuel injectors, which are delicate and expensive components of the engine, may become partially clogged.
As for the (EGR) valve itself, soot and grime may prevent it from properly, opening and closing. Therefore, If it becomes stuck in the closed position, it will lose all function. Consequently, the vehicle will continue to run properly, however it will emit nitrogen oxides at levels, beyond the threshold.
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. Consequently, carbon may be plugging up the exhaust port.
- Rough idle or misfiring because, the 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 valve is not closing and is creating a, vacuum leak into the intake manifold.
An (EGR) Valve, Stuck Open
So, when the (EGR) is stuck open, it will lead to a vacuum leak. Consequently, causing inefficient combustion, hesitation, rough idling and even stalling. The reason for this is, that the engine cannot combust on the carbon dioxide, emitted from the tailpipe. Because, an open (EGR) valve causes, exhaust emissions to flood the combustion chamber; hence preventing it from functioning as it should. So, 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 stuck open.
An (EGR) Valve, Stuck Closed
This causes nitrogen oxide emissions to rise and the engine might start to knock. Because, a sharp knock occurs, when the fuel in the combustion chamber ignites; before the explosion in the cylinder reaches it. As a result, this leads to a disruption in, engine timing. So, when this happens, warm up your engine and rev it, then check if the (EGR) valve will move.
The (EGR) valve has changed design, many times over the years.
So, most older (EGR) systems use a vacuum regulated valve. On the other hand, newer vehicles tend to have an electronic valve, to control exhaust gas recirculation. So, at idle speed the valve, should look closed. As a result, there is no, (EGR) flow into the manifold.
The valve remains closed, until the engine is warm and is, operating under load. But, as the load increases and combustion temperatures start to rise; the valve opens and starts, to leak exhaust back into the intake manifold. Finally, this has a quenching effect that, lowers combustion temperatures and reduces the formation of (NOx).
Here are some of the changes, over the years:
- 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). So, 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. Furthermore, using (VVT) for (EGR) also, eliminates many of the problems associated with (EGR) valves. For example, carbon buildup and valve sticking or failure.
(EGR) Valve Testing
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 under hood emissions decal. Does it have, a ported vacuum switch or a solenoid? Follow the vacuum connections from the valve. Also, refer to a service manual or the under hood emissions decal, for vacuum hose routing.
So, there are several ways to troubleshoot an (EGR) system. Follow the (EGR) troubleshooting procedure, in a service manual. 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 the 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.
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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