Chapter 1 Routine maintenance and servicing

1595Ford Fiesta Remake4D•2 Fuel system - sequential electronic fuel injection engines1 General information andprecautionsGeneral informationThe fuel system consists of a fuel tank(mounted under the body, beneath the rearseats), fuel hoses, an electric fuel pumpmounted in the fuel tank, and a sequentialelectronic fuel injection system.The electric fuel pump supplies fuel underpressure to the fuel rail, which distributes fuelevenly to all injectors. A pressure regulatorcontrols the system pressure in relation toinlet tract depression. From the fuel rail, fuel isinjected into the inlet ports, just above theinlet valves, by four fuel injectors. The systemalso includes features such as the flushing offresh (ie, cold) fuel around each injector onstart-up, thus improving hot starts.The amount of fuel supplied by the injectorsis precisely controlled by the EEC IV enginemanagement module. The module uses thesignals derived from the crankshaft positionsensor and the camshaft position sensor, totrigger each injector separately in cylinderfiring order (sequential injection), with benefitsin terms of better fuel economy and lowerexhaust emissions.The EEC IV module is the heart of the entireengine management system, controlling thefuel injection, ignition and emissions controlsystems. The module receives informationfrom various sensors which is then computedand compared with pre-set values stored init’s memory, to determine the required periodof injection.Information on crankshaft position andengine speed is generated by a crankshaftposition sensor. The inductive head of thesensor runs just above the engine flywheeland scans a series of 36 protrusions on theflywheel periphery. As the crankshaft rotates,the sensor transmits a pulse to the system’signition module every time a protrusionpasses it. There is one missing protrusion inthe flywheel periphery at a pointcorresponding to 90° BTDC. The ignitionmodule recognises the absence of a pulsefrom the crankshaft position sensor at thispoint to establish a reference mark forcrankshaft position. Similarly, the time intervalbetween absent pulses is used to determineengine speed. This information is then fed tothe EEC IV module for further processing.The camshaft position sensor is located inthe cylinder head so that it registers with alobe on the camshaft. The camshaft positionsensor functions in the same way as thecrankshaft position sensor, producing a seriesof pulses; this gives the EEC IV module areference point, to enable it to determine thefiring order, and operate the injectors in theappropriate sequence.The mass air flow sensor is based on a “hotwire”system, sending the EEC IV module aconstantly-varying (analogue) voltage signalcorresponding to the mass of air passing intothe engine. Since air mass varies withtemperature (cold air being denser than warm),measuring air mass provides the module witha very accurate means of determining thecorrect amount of fuel required to achieve theideal air/fuel mixture ratio.Engine temperature information is supplied bythe coolant temperature sensor. Thiscomponent is an NTC (Negative TemperatureCoefficient) thermistor - that is, a semiconductorwhose electrical resistancedecreases as its temperature increases. Itprovides the EEC IV module with a constantlyvarying(analogue) voltage signal, correspondingto the temperature of the engine coolant. This isused to refine the calculations made by themodule, when determining the correct amountof fuel required to achieve the ideal air/fuelmixture ratio.Inlet air temperature information is suppliedby the inlet air temperature sensor. Thiscomponent is also an NTC thermistor - seethe previous paragraph - providing themodule with a signal corresponding to thetemperature of air passing into the engine.This is used to refine the calculations made bythe module, when determining the correctamount of fuel required to achieve the idealair/fuel mixture ratio.A throttle position sensor is mounted on theend of the throttle valve spindle, to providethe EEC IV module with a constantly-varying(analogue) voltage signal corresponding to thethrottle opening. This allows the module toregister the driver’s input when determiningthe amount of fuel required by the engine.Road speed is monitored by the vehiclespeed sensor. This component is a Hall-effectgenerator, mounted on the transmission’sspeedometer drive. It supplies the modulewith a series of pulses corresponding to thevehicle’s road speed, enabling the module tocontrol features such as the fuel shut-off onoverrun.Where power steering is fitted, a pressureoperatedswitch is screwed into the powersteering system’s high-pressure pipe. Theswitch sends a signal to the EEC IV module toreduce engine speed should the powersteering fluid pressure become excessivelyhigh.The oxygen sensor in the exhaust systemprovides the module with constant feedback -“closed-loop” control - which enables it toadjust the mixture to provide the best possibleconditions for the catalytic converter tooperate.The air inlet side of the system consists ofan air cleaner housing, the mass air flowsensor, an inlet hose and duct, and a throttlehousing.The throttle valve inside the throttle housingis controlled by the driver, through theaccelerator pedal. As the valve opens, theamount of air that can pass through thesystem increases. As the throttle valve opensfurther, the mass air flow sensor signal alters,and the EEC IV module opens each injectorfor a longer duration, to increase the amountof fuel delivered to the inlet ports.Both the idle speed and mixture are underthe control of the EEC IV module, and cannotbe adjusted. Not only can they not beadjusted, they cannot even be checked,except with the use of special Ford diagnosticequipment.PrecautionsWarning: Petrol is extremelyflammable - great care must betaken when working on any partof the fuel system. Do notsmoke or allow any naked flames oruncovered light bulbs near the work area.Note that gas powered domesticappliances with pilot flames, such asheaters, boilers and tumble dryers, alsopresent a fire hazard - bear this in mind ifyou are working in an area where suchappliances are present. Always keep asuitable fire extinguisher close to the workarea and familiarise yourself with itsoperation before starting work. Wear eyeprotection when working on fuel systemsand wash off any fuel spilt on bare skinimmediately with soap and water. Notethat fuel vapour is just as dangerous asliquid fuel; a vessel that has just beenemptied of liquid fuel will still containvapour and can be potentially explosive.Petrol is a highly dangerous and volatileliquid, and the precautions necessarywhen handling it cannot be overstressed.Many of the operations described in thisChapter involve the disconnection of fuellines, which may cause an amount of fuelspillage. Before commencing work, referto the above Warning and the informationin “Safety first” at the beginning of thismanual.When working with fuel systemcomponents, pay particular attention tocleanliness - dirt entering the fuel systemmay cause blockages which will lead topoor running.Note: Residual pressure will remain in the fuellines long after the vehicle was last used,when disconnecting any fuel line, it will benecessary to depressurise the fuel system asdescribed in Section 2.2 Fuel system -depressurisation 1Refer to Part B, Section 2.3 Fuel lines and fittings -general informationRefer to Part B, Section 3.