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    Ford Escort/Lynx 1981-1990 Repair Guide

    Exhaust Gas Recirculation System

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    Operation

    The Exhaust Gas Recirculation (EGR) system is designed to reintroduce small amounts of exhaust gas into the combustion cycle, thus reducing the generation of Nitrous Oxides (NOx). 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, altitude, engine vacuum, exhaust system backpressure, coolant temperature and throttle angle.

    A malfunctioning EGR valve can cause one or more of the following:



    Detonation
     
    Rough idle or stalling on deceleration
     
    Hesitation or surge
     
    Abnormally low power at wide-open throttle
     

    Basic Poppet or Tapered Stem Design

    See Figure 1

    The basic EGR valve has two passages in the base connecting the exhaust system to the intake manifold. These passages are blocked by a valve that is opened by vacuum and closed by spring pressure. Both the poppet or the tapered stem design function in the same manner.



    Click image to see an enlarged view

    Fig. Fig. 1: Basic poppet and tapered stem EGR valves

    Integral Backpressure Transducer EGR Valve

    See Figure 2

    This poppet-type or tapered (pintle) valve cannot be opened by vacuum until the bleed hole is closed by exhaust backpressure. Once the valve opens, it seeks a level dependent upon exhaust backpressure flowing through the orifice and in so doing, oscillates at that level. The higher the signal vacuum and exhaust backpressure, the more the valve opens.



    Click image to see an enlarged view

    Fig. Fig. 2: Integral backpressure transducer EGR valve

    Backpressure Variable Transducer EGR Valve

    See Figure 3

    This system consists of three components: a vacuum regulator, an EGR valve and a flow control orifice. The regulator modulates the vacuum signal to the EGR valve using two backpressure inputs. One input is standard vehicle backpressure and the other is backpressure downstream of the flow control orifice. The control chamber pick-up is in the EGR tube and the flow control orifice is integral with the upstream EGR tube connector.



    Click image to see an enlarged view

    Fig. Fig. 3: Exhaust gas flow in the backpressure variable transducer EGR system

    Testing

    Exhaust Gas Recirculation (EGR) Valve

    See Figure 4



    Click image to see an enlarged view

    Fig. Fig. 4: Some EGR valves may be tested using a vacuum pump by watching for diaphragm movement

    1. Start the car and let the engine reach normal operating temperature.
    2.  
    3. Turn the engine OFF and connect a vacuum tester (pump) to the EGR valve vacuum source port.
    4.  
    5. Turn the engine ON and idle the engine.
    6.  
    7. Slowly apply 5-10 in. Hg (16-33 kPa) of vacuum; if the engine idles roughly or stalls, the EGR valve is functioning properly.
    8.  
    9. If the engine does not idle roughly, replace the EGR valve.
    10.  

    REMOVAL & INSTALLATION



    See Figures 5 and 6

    1. Unplug the vacuum hose from the EGR valve.
    2.  
    3. If applicable, unplug the electrical connector and remove the Exhaust Valve Position (EVP) sensor. It may be secured by small screws.
    4.  
    5. If equipped, unfasten the nut that attaches the EGR tube to the valve, then separate the tube from the valve.
    6.  



    Click image to see an enlarged view

    Fig. Fig. 5: Unbolt the EGR valve from its base, then remove the valve and old gasket



    Click image to see an enlarged view

    Fig. Fig. 6: If installing the old valve, be sure to clean the gunk and build-up from all the passages

    1. Unfasten the nuts/bolts securing the EGR valve and remove the valve. Discard the gasket.
    2.  

    To install:
    1. Clean the EGR valve gasket mating surfaces.
    2.  
    3. Install a new gasket and the EGR valve.
    4.  
    5. Install and tighten the EGR valve nuts/bolts to 18 ft. lbs. (25 Nm).
    6.  
    7. If equipped, attach the EGR tube to the valve and tighten the valve-to-tube nut.
    8.  
    9. If equipped, install the EVP sensor and attach its electrical connection.
    10.  

     
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