Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation:

EGR Solenoid Wiring Circuit:

PURPOSE
The Exhaust Gas Recirculation (EGR) system is designed to decrease NOx (Oxides of Nitrogen) in exhaust emissions.

It does this by introducing exhaust gas, which contains very little oxygen, into the intake manifold. The exhaust gas will not support combustion, but does occupy volume, reducing the total amount of air/fuel mixture which burns in the cylinder. This reduces combustion temperatures.

OPERATION
The EGR valve is opened by ported vacuum to allow exhaust gas to flow into the intake manifold. The exhaust gas then flows with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion may not occur. For this reason, very little exhaust gas is allowed to pass through the valve, and none at idle. The EGR valve is usually open when the engine is at normal operating temperature.

RESULTS OF INCORRECT OPERATION

With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:
^ Engine stops after cold start.
^ Engine stops at idle after deceleration.
^ Vehicle surges during cruise.
^ Rough idle.
^ Emission test failure.

If the EGR valve should stay open all of the time, the engine may not idle.

Too little or no EGR flow allows combustion temperatures to get too high, this could cause:
^ Spark knock (detonation).
^ Engine overheating.