Exhaust Gas Recirculation: Description and Operation

EGR Valve:

PURPOSE
The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by reducing combustion temperatures.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With fuel/air mixture thus diluted, combustion temperatures are reduced.

RESULTS OF INCORRECT EGR SYSTEM OPERATION
Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:

- Engine stalls after cold start.
- Engine stalls at idle after deceleration.
- Vehicle surges during cruise.
- Rough idle.

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause:

- Spark knock (detonation).
- Engine overheating.
- Emission test failure.
- Fuel economy.