Contents: Device ⤓ Examination ⤓
Device
Exhaust gas recirculation is used to reduce peak flame temperatures in the combustion chambers. A small amount of exhaust gas is removed from the exhaust manifold and re-introduced into the intake manifold, where it is mixed with the supplied air-fuel mixture and enters the cylinder. With lower combustion temperatures, the nitrogen oxide content of the exhaust gases is reduced.
The EGR system consists of an EGR valve that regulates the flow of exhaust gases, as well as various vacuum and electrical control devices that prevent the EGR system from being triggered in a timely manner. There is no need for an EGR when the engine temperature is low enough to reduce the flame temperature in the engine. Using an EGR in this case would lead to unstable engine operation, so the EGR function is disabled by either a thermal valve or a fuel injection computer (which controls the coolant temperature). In addition, the EGR is also disabled at idle speed on a warmed-up engine to prevent unstable speed or "jerking" when pressing the accelerator (gas) pedal.
A decrease in combustion temperature also leads to some reduction in power. For this reason, when the engine switches to the fully open throttle driving mode, the EGR function is disabled. Normally, the vacuum acting on the EGR valve overcomes the tension force of the spring inside the valve and holds it open. When the throttle valve is fully open, the vacuum acting on the EGR decreases, and the spring closes the valve. A common symptom of a faulty EGR is a slight detonation of the engine with a partially open throttle valve, most noticeable under load, i.e. when climbing a hill or when transporting several passengers. The EGR valve can cause unstable and uneven idle speed. If the engine is adjusted correctly and other causes (vacuum failure, poor spark plug wires) are eliminated, then when unstable idle speed appears, the fault lies in the EGR.
Examination
With the engine cool, disconnect the throttle body vacuum hose.
Plug the pipe from which the hose was removed. Start the engine. On fuel-injected engines, the EGR system will not maintain vacuum when the engine is cold and idling.
Warm up the engine to normal operating temperature. Before checking, the coolant temperature should be 80-85°C. Using the pump, create a vacuum of 30-43 mm Hg. The EGR system should maintain the vacuum, while idling will not be accompanied by noticeable changes.
On a fuel-injected engine, let the warm engine idle as described above. Create a vacuum of 83 mm Hg and listen to the engine. When the desired vacuum is reached, the idle will become unstable, uneven, and the engine may even stall as soon as the EGR valve opens and allows exhaust gas to pass through. The system should maintain a vacuum with the valve slightly open.