Tip & How-To about Mercedes-Benz E-Class
1.6) EGR - Exhaust Gas Recirculation valve (actuator)
What is it? This is a device that reduces engine emissions of nitric oxides by allowing a measured amount of exhaust gas to re-enter the intake manifold and mix with the air prior to entering the cylinders. The EGR can be vacuum (older types) or electrically driven (modern) or a hybrid combination of both (intermediate age). Adding inert exhaust gas to the intake charge artificially enriches the fuel air mix (by diluting the air) and thereby reduces ignition temperatures associated with lean running conditions
Where is it located? The EGR is associated with the intake manifold. The EGR is sited at a point of contact with both the exhaust and intake manifolds. If the exhaust manifold is remote to the inlet manifold, for example onthe other side of the engine, an exhaust feed pipe leading from the exhaustmanifold to the EGR is provided.
How does it work? Generally intake manifold vacuum acting on a diaphragm draws up on a pintle valve to open a connection between a (usually round) entry port for the exhaust gases and an exit port (usually rectangular) to the intake manifold. The opening of some modern EGR valves iscompletely under the (ECU) control of an electrical motor/solenoid. Since an open EGR port effectively acts as a vacuum leak in the inlet manifold leading to potential starting and idling difficulties, the EGR valve operation is often impeded by an electrical over-ride at cold/start-up until the engine reaches running temperature and high revs. The ECU takes signals from the coolant temperature sensor to determine when the engine is hot before allowing the EGR to function. In some cases, a differential pressurefeedback exhaust (DPFE) sensor, connected to pipes on the exhaust feed to the EGR, informs the ECU when and by how much the EGR should be open.
NEXT 1.6b) EGR faults and how to fix
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