Exhaust Gas Recirculation: Description and Operation

Typical Vacuum Operated EGR System


The Exhaust Gas Recirculation System (EGR) is designed to reintroduce exhaust gas into the combustion cycle lowering combustion temperatures and reducing the formation of Nitrous Oxide. There are four basic types of EGR valves:

^ The Integral Backpressure Transducer EGR Valve (9D448)

^ The Ported EGR Valve (9D475)

^ The Electronic EGR Valve (9F483)

^ The Valve and Transducer Assembly EGR Valve (9H495)



Typical components connected with in the system are:


^ EGR Valve.

^ PVS and or TVS.

^ Carburetor EGR port


The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration and is controlled by various factors such as engine speed, engine vacuum, exhaust system backpressure, coolant temperature and throttle angle depending on the calibration. All EGR valves are vacuum actuated. The vacuum diagram is shown on the emission decal for each calibration.


Figure 1 shows a typical EGR valve installation.










Typical Backpressure Variable Transducer (BVT) System


The BVT system is used on most 1.9L and 2.3L passenger car applications. A typical BVT control system is shown in Figure 2. it Consists of three components; a vacuum regulator (9J431), EGR valve (9D475) and a flow control orifice.



The regulator modulates the vacuum signal to the EGR valve using two backpressure inputs. One input is the standard vehicle backpressure and the other is the backpressure downstream of the flow control orifice. The control chamber pickup is in the EGR tube and the flow control orifice is integral with the upstream EGR tube connector.