Chapter 1 Routine maintenance and servicing

1595Ford Fiesta Remake4B•2 Fuel system - central 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 central fuelinjection (CFi) system.Fuel is supplied from the tank by an integralelectric fuel pump (and combined fuel gaugesender unit). The fuel is passed through an inlinefilter within the engine compartment, thento the fuel injection unit. The fuel is maintainedat the required operating pressure by apressure regulator unit.The CFi unit itself is a relatively simpledevice when compared with a conventionalcarburettor. Fuel is injected by a singlesolenoid valve (fuel injector) which is mountedcentrally on top of the unit. It is this featurewhich gives the system CFi (or Central Fuelinjection) its name (see illustration).1 Fuel injector assembly2 Fuel pressure regulatorassembly1.3 Exploded view of the CFi unit3 Fuel feed connector4 Intake air temperaturesensorThe injector is energised by an electricalsignal sent from the EEC IV enginemanagement module. When energised, theinjector pintle is lifted from its seat, andatomised fuel is delivered into the inletmanifold under pressure. The electricalsignals take two forms of current - a highcurrent to open the injector, and a low currentto hold it open for the duration required. Atidle speed, the injector is pulsed at everyother inlet stroke, rather than with everystroke as during normal operation.The air-to-fuel mixture ratio is regulated bythe EEC IV module, based on inputs from thevarious engine sensors. No adjustments tothe fuel mixture are possible.The throttle plate control motor (mountedon the side of the CFi unit) regulates the idlespeed by reacting to the signals sent by theEEC IV module. The signals are calculated bythe values and information provided from theengine sensors. When the throttle positionsensor indicates that the throttle is closed, themodule enters the idle speed mode ordashpot mode (according to engine speed).The module maintains the idle speed at a5 Throttle-plate controlmotor6 Throttle position sensor7 Fuel injector wiringconstant value, making minor adjustments asnecessary for different loads and conditions.The base idle speed can only be adjusted by adealer or fuel injection specialist with thenecessary equipment to link up to the enginemanagement module.To prevent the engine from running on (ordieseling) when it is switched off, the EEC IVmodule sends a signal to the throttle platecontrol motor, to fully close the throttle plateand return it to its preset position ready forrestarting. When the ignition is switched onto restart the engine, the motor repositionsthe throttle plate to the position requiredaccording to the prevailing conditions.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 to determine enginetemperature, speed and load, and thequantity of air entering the engine. Thesensors also inform the module of throttleposition, inlet air temperature and exhaust gasoxygen content. All the information suppliedto the module is computed and comparedwith pre-set values stored in it’s memory, todetermine the required period of injection.Information on crankshaft position andengine speed is generated by the distributoron pre-1990 CVH engine models, or by acrankshaft position sensor on all othermodels. The inductive head of the crankshaftposition sensor runs just above the engineflywheel and scans a series of 36 protrusionson the flywheel periphery. As the crankshaftrotates, the sensor transmits a pulse to thesystem’s ignition module every time aprotrusion passes it. There is one missingprotrusion in the flywheel periphery at a pointcorresponding to 90º 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.Engine temperature information is suppliedby the 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,corresponding to the temperature of theengine coolant. This is used to refine thecalculations made by the module, whendetermining the correct amount of fuelrequired to achieve the ideal air/fuel mixtureratio.Inlet air temperature information is suppliedby the inlet air temperature sensor. Thiscomponent is also an NTC thermistor - seethe previous paragraph - providing the EEC IVmodule with a signal corresponding to thetemperature of air passing into the engine.