EGR System: Description

The Exhaust Gas Recirculation (EGR) system is designed to reintroduce small amounts of exhaust gas into the combustion cycle thereby lowering combustion temperatures due to lower concentrations of oxygen. This lowering of combustion temperatures reduces the amount of NOx emissions produced by the engine. The amount of exhaust gas recycled and the timing of the cycle are controlled by such factors as engine vacuum, exhaust system backpressure, altitude, temperature, throttle angle and engine speed.

Typical systems consist of an EGR valve, carburetor EGR port, vacuum reservoir , check valve, and a Ported Vacuum Switch (PVS) and/or a Temperature Vacuum Switch (TVS).

Ford Motor Co. uses 4 basic types of EGR valves. They are integral backpressure EGR valve, ported EGR valve, electronic EGR valve and backpressure transducer EGR valve which is a modified Port EGR Valve with separate backpressure variable transducer.

The EGR Backpressure Variable Transducer (BVT) system is used on few models. This system combines a ported EGR valve with a backpressure variable transducer to control NOx emissions. Typical components included in this system are an EGR valve, a PVS or TVS and a carburetor EGR port or vacuum tank vacuum source.

Models with Electronic Engine Control (EEC) systems use an electronic EGR valve with a EGR Valve Position (EVP) sensor controlled by a vacuum solenoid assembly. In addition, this system uses an exhaust cooler which uses coolant to reduce the temperature of the exhaust flowing through the EGR valve.

Some selected 2.0L and 2.3L engines use an EGR valve and transducer assembly which consists of a ported EGR valve and a pressure tap to provide a backpressure signal to a remote backpressure transducer. This system operates the same as the integral backpressure transducer valve system. Functional checks are also the same on this system.